Selective call, paging and priority signalling system

ABSTRACT

A selective calling, paging and priority signalling system for two way communications between at least one primary and a plurality of remote stations. An automatic selective calling mode is provided in which the primary station operator enters the address of the desired unit and activates his microphone. Unmuting data packet will then be transmitted to the addressed remote station, unmuting the remote station. When the transmission ends, a mute data packet is transmitted, remuting the remote station.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to data communication systems and inparticular to an improved data system for selective calling, paging andpriority signalling particularly well adapted for use in multiple unitradio communication systems capable of voice and data communications.

2. Description of the Prior Art

In the prior art, multiple unit radio communications systems utilizecomplex signalling systems to provide both voice and data communicationscapability. Some provide one way status indication capability andacknowledge but with very inflexible formats which limit usefulness.Existing systems utilize structures which are very expensive tomanufacture and provide for limited sensitivity in most RF environments.Further, previous systems have been organized around a coding structurethat viewed the terminal device as one which responded to a set ofdiscrete commands. The terminal was designed to perform some arbitraryset of operations when a defined command code activated it. Thisresulted in an inflexible system. In addition, prior art communicationssystems, because of inflexible format, did not have automatic selectivecalling, dynamic regrouping and transmit control capability.

SUMMARY OF THE INVENTION

It is an object of the invention, therefore, to provide an improvedcommunications system for selective calling, paging and prioritysignalling particularly well adapted for transfer of data over an audiochannel of a multiple unit radio comunications system.

It is another object of the invention to provide an improvedcommunications system which permits a priority alert havingidentification of individual remote unit with acknowledgement andpriority monitoring capability.

It is yet another object of the invention to provide a communicationsystem having automatic selective calling dynamic regrouping andtransmit control capability.

Briefly, according to the invention, a method of selective calling isprovided in a communication system having a primary station including anaddress entry port, and a plurality of remote stations. Each remotestation has a predetermined station address stored in a station addressregister. The method comprises, at the primary station, the steps ofentering a desired station address into the address port and thentransmitting a first command signal containing a predetermined controlcode and the desired station address in response to initiating a voicetransmission. Subsequently, a second command signal is transmittedcontaining a second predetermined control code, and the desired stationaddress in response to the conclusion of the voice transmission. At theremote stations, the method comprises, receiving the transmitted firstcommand signal, then detecting when the desired station addresscontained in the received first command signal is the same as thepredetermined station address stored in the station address register andunmuting the remote station receiver in response thereto. The methodfurther comprises receiving the transmitted second command signal,detecting when the desired station address contained in the receivedsecond comand signal is the same as the predetermined station addressstored in the station register and muting the remote station receiver inresponse thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further object and advantages thereof, may best beunderstood by reference to the following description when taken inconjunction with the accompanying drawings.

FIG. 1 is a block diagram of a multiple unit radio communications systemwhich may utilize the present invention.

FIG. 2 is a diagram of the preferred data packet structure according tothe invention.

FIG. 3 is a diagram of the preferred encoded data packet structureaccording to the invention.

FIG. 4 is a block diagram of a novel base unit data communicationscontroller that may advantageously utilize the invention.

FIG. 5 is block diagram of a novel mobile unit control circuit that mayadvantageously utilize the present invention in conjunction with thebase data communications controller of FIG. 4.

FIG. 6 is a flow diagram of the RESTART routine of the base unitcomputer program for the invention.

FIG. 7 is a flow diagram of the PSK RECEIVE routine of the base unitcomputer program for the invention.

FIGS. 8A and 8B form a flow diagram of the PACKET PARSING routine of thebase unit computer program for the invention.

FIGS. 9A, 9B and 9C form a flow diagram of the KEYBOARD HANDLER routineof the base unit computer program for the invention.

FIGS. 10A, 10B and 10C form a flow diagram of the COMMAND routine of thebase unit computer program for the invention.

FIGS. 11A and 11B form a flow diagram of the COMMAND TRANSMIT routinefor the base unit computer program for the invention.

FIG. 12 is a flow diagram of the RETRANSMISSION routine of the base unitcomputer program for the invention.

FIG. 13 is a flow diagram of the POLL EXIT routine of the base unitcomputer program for the invention.

FIG. 14 is a flow diagram of the DATA TRANSMIT subroutine of the baseunit computer program for the invention.

FIG. 15 is a flow diagram of the PROM PROGRAMMER HANDLER routine of thebase unit computer program for the invention.

FIG. 16 is a flow diagram of the START routine of the mobile unitcomputer program for the invention.

FIG. 17 is a flow diagram of the EXT routine of the mobile unit computerprogram for the invention.

FIG. 18 is a flow diagram of the TRANS-EMERG routine of the mobile unitcomputer program for the invention.

FIG. 19 is a flow diagram of the P1CHK-HUBCHK routine of the mobile unitcomputer program for the invention.

FIG. 20 is a flow diagram of the TIMCHK routine of the mobile unitcomputer program for the invention.

FIG. 21 is a flow diagram of the EMRMON routine of the mobile unitcomputer program for the invention.

FIG. 22 is a flow diagram of the TONES routine of the mobile unitcomputer program for the invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, is illustrated the preferred embodiment of a multiple unitradio communications systems that communicates both data signals andvoice signals between dispatchers at primary stations 50, 52, (i.e.,base stations) and secondary radios (i.e., mobile in the preferredembodiment) which may utilize the invention. The radio systemillustrated provides enhancement to normal voice RF systems but theinvention is not limited to RF systems. The system is processor basedsuch that all the control operations and signalling are performed insoftware, allowing a portable and modular system that is flexible,reliable, and inexpensive to manufacture.

As illustrated by FIG. 1, the system configuration is highly flexible.Each station includes a dispatcher control console 44, 46, 48 and a basedata controller 40, 38, 36 and 34, each having a 12 key keyboard and afour digit display (not shown). A base data controller 40, 38, 36, 34 iscoupled to each console unit 44, 46, 48, 32, as shown. Data and voicesignals are coupled from the console 44, 46, 48, 32 to a base station50, 52 by wire lines. The base stations 50, 52 each include a radiotransmitter and receiver for communications via a radio frequency (RF)channel to remote (mobile) radios 60, 62 and 64. The mobile radio 60, 62and 64 may be any suitable conventional radio such as an FM radio incombination with a mobile data control unit (not shown) according to theinvention.

Voice communications with the mobile radios 60, 62, 64 is established bymeans of the dispatcher console 44, 46, 48, 32 while data communicationsare established by means of the base data controllers 40, 38, 36, 34.Received data signals can be displayed on the four digit display of thebase controller. Data signals transmitted by the base data controllers40, 38, 36 and 32 may be entered from the keyboard or may beautomatically generated as, for example, in the case of automaticacknowledgement signals.

The base data control unit may be utilized in numerous configurations.As shown, data controller 40 is coupled to the second data controller38, which are individually coupled to a dispatcher console 44 anddispatch console 46, respectively. The consoles 44, 46 are both coupledas shown, to the base station 50. Thus, several base data controllerscan function in configuration with several console units using a singlebase station. An alternative configuration is shown with the datacontroller 36 coupled to a single console 48 which is coupled to a basestation 42. All three data control units are coupled via a bus 12, asshown, to a master console 32 permitting each base data controller andbase station to be monitored with the master console 32 and a base datacontroller 34 coupled thereto. A conventional printer 30 is provided topermit logging of any of the data information desired.

The radio communications system in FIG. 1 is particularly well adaptedfor dispatch type applications, where a dispatcher at a base stationcommunicates with operators of a fleet of mobile radios. In suchdispatch radio communications systems, there may be one or more RFchannels that are shared by several hundred mobile radios. Therefore, itis desirable that some of the communications between the dispatcher atthe central station and the operators of the mobile radios be providedby means of data communications so that use of each RF channel is moreefficient.

The data signals communicated between the base stations 50 and 52 andthe mobile radio 60, 62, 64 include a bit synchronization portion, asynchronization word, and an information word. The bit synchronizationportion may consist of a 1, 0 alternating pattern for allowing areceiver to attain clock synchronization. The synchronization word mayconsist of any suitable correlatable bit pattern. The information wordmay consist of an address, commands, and/or status information. Codingtechniques are used for error correction and detection to provide lowfalsing rates and high sensitivity. The preferred embodiment of thesignalling system utilizes PSK modulation at 600 bits per second with a1500 Hz carrier using coherent detection. The data transfer isaccomplished using a 32 bit data packet, as illustrated in FIG. 2. The32 bit data packet is encoded to a 176 bit encoded data packet beforetransmission, as shown in FIG. 3. This encoded data packet includes 24bits of data modulated to allow for clock recovery synchronization asshown in block 74 of FIG. 3, and consists of alternating ones and zeros.In addition, a 40 bit fixed synchronization code word is appended asshown in block 74 of FIG. 3. The 32 bit data packet is encoded by firstgenerating a 48 bit inner code word by appending a 16 bit cyclicalredundancy check code to the 32 bit data packet, as shown at 72 of FIG.3. This 48 bit inner code word is further encoded using a half rateconvolution encoder. This produces a 112 bit coded word. Thus, a 176 bitencoded data packet is generated as illustrated in FIG. 3.

Upon reception, an exact copy of the original 32 bit data packet isextracted from the 176 bit encoded data packet using conventionaldecoding methods. The structure of the codes insures that theinformation can be extracted correctly even if some of the encoded datapacket has been corrupted by channel disturbances. Bit synchronizationis obtained using the 24 bit preamble providing a pattern to permitextraction of bit clock information. The word synchronization isaccomplished by continuously comparing the last 40 receivedsynchronization bits with a fixed synchronization code word and when apredetermined number (35 in the preferred embodiment) of the 40 bitsmatch the synchronization code word bits synchronization is detected.Detection of the synchronization word indicates that the 112 bits of theencoded data word follow immediately. The next 112 bits of the encodeddata are stored and then decoded. Transmission time for the basic 176bit encoded data packet is 290 milliseconds in the preferred embodiment.

The general format of the information word (i.e., command data packet)is shown in FIG. 2, which includes a general description of each field.This basic command packet is only one of several formats that can beused, for example, a simple data block is another possible format inwhich the first 31 bits are free formatted. In the command packet bit 31(see FIG. 2) is a data command indicator bit used to identify the packetas a command or control format or a free format data packet. If the bitis zero, the packet is considered to be a command or control packet andfollows the format of FIG. 2. If the bit is 1, the packet is a freeformat data packet. Free format data packets are preceded by a "header"packet of the command type identifying the source or destination of thefree format packet and containing the proper OP code and format for thepackets that follow. Thus, data packets with 31 bits of data may beconcatenated for intense information transfer, such as text.

The bit indicated in FIG. 2 as bit 30 is the acknowledge/no acknowledgebit. This bit is used by the destination unit for acknowledgementpurposes and is OP code dependent. If the acknowledge/no acknowledge bitis equal to zero, the destination unit will not acknowledge the command,but if the acknowledge/no acknowledge bit is one, the unit shouldacknowledge unless the OP code indicates a request or interrogation typecommand. Thus, certain commands transmitted from either the base or themobile unit of the preferred embodiment are automatically acknowledgedby the receiving unit. In addition, in the preferred embodiment,automatic re-transmission is provided for a programmed number of timesin situations in which no acknowledge has bee received.

The next indicator bit, indicated in FIG. 2 as bit 19, is theoutbound/inbound bit (O/I) used to route data packets. If the O/I bit iszero, the data packet is inbound directed and if the O/I bit is a one,the data packet is outbound. Both the mobile and the base units of thepreferred embodiment utilize both states of the O/I bit.

The OP code field of the command packet, shown as bits 24 through 28 ofFIG. 2, is used to address a specific internal register of thedestination address thereby making it possible to specify a particularcommand or control operation. Any specific set of instructions may bedefined up to 64. In the preferred embodiment, there are several commandinstruction codes defined and several data type codes.

Each command data packet also contains an argument field, indicated inFIG. 2 by bits 16 through 23, used primarily for data transfer. Forexample, in the preferred embodiment, status, data, or controlinformation is transferred in the argument field. It is also used as aspecific command/control operation when combined with the OP code field,so that up to 256 unique commands can be implemented with each OP code.

The remaining 16 bits of the command data packet, bits zero throughfifteen in FIG. 2, are the address field of the 32 bit packet. Theaddress field is partitioned into our hexadecimal digits, as shown. Thisprovides up to 65,536 unique addresses, identifying the sending unit forinbound packets, and identifying the destination unit for outboundpackets. In the preferred embodiment, ten thousand unique unitidentification codes are used permitting the system to be partitionedinto ten fleets with up to 100 unique codes per fleet. Each mobile unitis pre-programmed to contain a unique unit, group and fleetidentification code.

An outbound wild card mode of addressing permits a flexible method ofgroup, fleet, and all addressing that may be dynamically configured. Inthis mode, the hexadecimal F is used in any address partition to signifya match or wild card. When encountering a wild card in any of the fourhexademical positions, the unit decoder will match that position withthe same position of the pre-assigned unit identification address. Thus,for example, an address of ZFFF would be a fleet call to fleet 2, andFFFF would be an all call.

An outbound direct addressing mode permits addressing group and fleetswhile allowing units to be members of any group or fleet. In this mode,the hexadecimal E is placed in the most significant digit position ofthe address field (digit 3) and the fleet address is placed in the nextdigit position (digit 2) followed by a two digit BCD group number toaddress a group. The hexadecimal F can be placed in the group positionto address a fleet and FFFF can be used to address all fleets.

In the preferred embodiment, the base unit has the capability tore-group mobile units at any time such that the group code becomes, inaffect, a soft identification number. For example, suppose thedispatcher wishes to have a conversation with a particular group. But,that there is one member of that group he would like to exclude. He maytemporarily move that member to another group, proceed with theconversation, and then return the individual to the group. Each mobileunit may default to the fixed preprogrammed group code on power on.

In the preferred embodiment, the argument field is often used fortransmission of status information wherein there are two levels ofstatus used. The first level is called operator status, since it isgenerally associated with the operator of the mobile unit. The secondlevel is called alternate status and requires an optional interfacecircuit in the mobile unit. Operator status may be initiated from themobile unit by various methods. A change in a set of status switches mayinitiate the transmission of status in cases in which the statusswitches are exclusive and interlocked. Current status is also sent withevery voice transmission and priority alert transmission. Each base unitis equipped with status keying, which allows for display and audioselectivity based upon the received status of a mobile unit. The key maybe dynamically configured by the base operator so that, for example, thebase audio may be selected to unmute for a particular mobile status. Thestatus switches may also represent message transmissions wherein messagetransmissions use momentary switches to indicate a transient conditionwhile status transmission user interlock switches to indicate a heldcondition. The base operator may also interrogate any mobile for circuitoperator status.

A total of eight independent operator status bits are available for eachmobile unit. Thus permitting a total of 128 operator status states. Thealternate status option provides up to 7 bits of independent alternatestatus which are readable and setable from the base unit.

The system also provides enhanced selective calling and paging, whichcan be automatic. With this feature, each call to a unit, group or fleetcontains a preamble and a postamble code to unmute and remute,respectively. The base operator therefore simply enters anidentification code and then talks as normal to the mobile unit whichwill automatically reset after the conversation. Or a mobile operatormay transmit a voice message which will display the unit number on theconsole where the base operator then simply presses the transmit switchto selectively respond to the calling mobile. This mode of operation isreferred to as AUTO SEL CALL. Paging is provided with automaticacknowledge to activate internal and external alarms at the mobile suchas light, horns, and tones.

A priority alert capability exists in which the mobile unit can beactivated to the priority alert by an external switch which has priorityover any other radio functions. Priority alert will transmit immediatelyupon activation regardless of activity on the channel and up to twentydata packet retransmissions will occur if the mobile unit does notreceive an acknowledge. The base unit will give special treatment tothis priority alert transmission. When a priority alert transmissionoccurs, the current operator status of the initiating unit is forwardedto the base unit automatically. There are, in addition, two possibleacknowledge packets that can be used with priority alert. The first isthe normal acknowledge which simply handshakes the original unit. Thesecond also handshakes the originating unit, but, in addition, enablesthe mobile transmitter for a preset period of time permitting the baseoperator to monitor that unit. This feature is referred to as emergencymonitoring. An emergency monitor acknowledge also disables any othermobile units on the channel from voice transmissions for the duration ofthe preset period.

There are a number of major options and configurations which arepossible in the preferred embodiment based on the signalling systemdescribed. These options and configurations are selected by means of aPROM code plug which is in both the base and mobile units. Varioussystem perimeters are also contained in the code plug.

Referring now to FIG. 4 there is illustrated a preferred embodiment of abase unit data controller. This base unit of FIG. 4 utilizes amicrocomputer (MPU) system in conjunction with system firmware andperipheral devices to provide a terminal system for mobile and portableapplications. The microcomputer 100 performs all of the necessarycontrol and interface logic as well as all of the signalling functionsincluding modulation and demodulation, encoding and decoding, displaycontrol, keyboard handling, printer interfacing and mobile code plugprogramming.

As shown in FIG. 4, the base unit includes an MPU 100, which in thepreferred embodiment, is an eight bit microcomputer (e.g., a MotorolaMC6803). Internal to the MPU 100 is a clock utilizing a crystal 120,coupled as shown to the MPU 100, to produce a system clock frequency of4.9152 megahertz in the preferred embodiment and which is dividedinternally to yield an MPU frequency of 1.2288 megahertz. A keyboardsystem is coupled to the MPU 100 consisting of a 12 key keyboard 102coupled to a key encoder 104 which is coupled, as shown, to the addressbus 108 and the data bus 106, as shown. The key encoder 104 includes astorage function and provides interrupts to the processor whileincluding key debouncing circuitry. The system firmware consists of allthe software necessary for the system operation which is stored in aread only memory (ROM) 112 which is coupled to the address bus 108 andthe data bus 106, as shown. A random access memory (RAM) 114 is coupledto the MPU 100 via the data bus 106 and the address bus 108, as shown,for use as a serial interface buffer and for identification memory. Asystem code plug 110 is coupled to the MPU 100 via the address bus 108and the data bus 106 to store system variables and particularoperational characteristics and options of individual units. A real timeclock 86 together with a crystal 88 is coupled to the output ports 96,92 and to the input port 94, as shown, primarily to provide timeinformation for logging. Interface circuitry consisting of a PSKbandpass filter 126, a limiter 124, audio muting relay 132, mic mutingrelay 134, audio alert generator 136, multi-terminal control logic 140and external interface logic 130 is coupled, as shown, to the MPU 100.Additional interface circuitry is provided by the RS 232 serialinterface 84 coupled with voltage converter 82 and power supply 80 tothe MPU 100, as shown. A PROM programmer interface 90 is provided topermit programming identification codes of mobile units and is coupled,as shown, to the output port 92 and the input port 94. Also provided isdisplay circuitry 98 which consists of a display controller for sevensegment LED displays and eight LED status indicators (not shown). Thisbase unit structure as shown in FIG. 4, provides the capability todirectly interface to a wide variety of RF communication systems.

The display system 98 consists of a four digit LED display and eightindividual LED indicators. The display is used for data display of allinbound and outbound identification codes including unit, group, andfleet. The display is also used in editing, data entry, code plugprogramming, status retrieval and setting as well as displaying anyinbound data. The display is driven from the microprocessor system andwill accommodate multiple controllers for console applications.

The keyboard system is used for data entry, display editing, commandentry and execution. Any and all terminal control is accomplishedthrough the keyboard system and the microphone push to talk switch. Thekeyboard 102 has two basic keyboard entry modes; upper and lower case.The lower case mode is used to enter identification code numbers andcommand data. The upper case mode is used in command entry and eventualexecution. The base operator has complete control of the data systemthrough the keyboard system.

A real time date clock 86 provides time and date to permit display ofthe time and date of any and all of the transactions that occur on thesystem. It is primarily used in the logging system but may also be usedas a clock or event scheduler. A specific program necessary to definethe particular characteristics of each individual system is contained ina PROM code plug, 90. There are many variables related to a particularsystem which are defined by the data in this code plug. All the keycommand definitions to be used in the system are defined by the data inthe code plug which must be programmed prior to use. The functionsdefined by code plug data will be discussed in greater detailhereinafter.

Data squelch is provided for the system so as to blank the audio of datatransmissions. The data muting function is provided by software in theMPU 100 and by the audio muting relay 132. In addition to data squelch,the audio muting relay 132 is utilized to perform conventional audiomuting. The mute and unmute operation may be keyed off a particularstatus or identification code.

Each base unit is capable of addressing unit ID codes from 0 to 9999. Inaddition, a shared system can be structured in which the range is from 0to 999 wherein the most significant digit is used as a fleetidentification, thus allowing up to 10 fleets or a signal channel. Insystems which use multiple base units to accommodate multipledispatchers, each base unit can have keyboard programmable upper boundand lower bounds of accessible ID codes and the range of codes may bedynamically allocated. The base operator thus, would not be allowed toaccess any codes outside of the current range setting, nor will anyinbound data be processed outside the range. In addition, audio mutingmay be used so that a particular operator will only hear transmissionswith ID codes within the selected range.

Many multiple unit communication systems have multiple transmitterswhich are not always co-located. The base unit provides PTTidentification at the beginning and/or end of either a voice or a datatransmission. The system code plug determines the desired mode and alsocontains the four digit ID code. Thus, a particular base unit canidentify all mobile and base transmissions and the ID code can be usedin logging to indicate wich unit received or transmitted data. Insystems where multiple units are used on the same RF channel, control isprovided by means of code plug data to prevent multiple simultaneousacknowledge transmissions to mobile units. One unit is designated as themaster and the remaining units are designated as slaves, such that themaster is programmed to transmit all acknowledge data packets. Theacknowledged transmissions can also be programmed to be dependent on thekeyboard defined unit code bound and status key. The normal mode ofoperation for base unit commands utilize the automatic acknowledgefeature with re-transmissions. However, the system may also be used withone way modes where the base unit is configured by the code plug totransmit commands only once and not to except an acknowledge when themobile units in the system are set up in the same configuration mode.

The transmission time of a base data packet is approximately 325milliseconds providing for radio transmitter turn on delays. However,most systems have inherent delays associated with repeaters tone remoteand others that must be anticipated before the actual data packet can betransmitted. To allow for these variable delays, the base unit willgenerate based on the code plug information, transmission delays from100 to 1500 milliseconds in 100 millisecond increments. The transmitterwill send silent carrier during the delay to minimize data noise on thechannel and allow easy interfacing into tone remote systems. All mobileand base units in a given system must have the same system delay.

The base unit will display all incoming PTT identification codes andstatus indications. The status indicators will reflect the currentstatus of the particular unit. The PTT ID transmissions have displaypriority over any commands in progress. For example, if the baseoperator is in the process of entering a number and a PTT ID isreceived, the display will show that ID. The same is true for commands.Any command in progress will be aborted if a PTT ID is received. Thismode of operation will only occur if a PTT ID receive option is selectedin the code plug. When an ID is received and properly decoded, it istested against the current bounds. If the code falls within the bounds,the ID will be displayed and put into memory for further processing andsent to the logging system for printout.

A priority alert transmission mode is provided which has absolutepriority over any terminal transactions. The base unit will display theunit code of the mobile generating the alert. The display will flash theID code and any status indications as well as sound an audio tone. Toclear the system of a priority code the base operator must press theclear switch. Priority alert may be stacked in a LIFO memory andrecalled by a recall command so that multiple priority alerts may occursimultaneously without loss of data. However, if the base unit iscurrently in the priority mode and a new priority is received, the newpriority ID will take over the display. The previous priority may belater recalled from memory. Even though a priority alert will lock outthe display from any further use, data packets can still be received andacknowledged. All data will also continue to be sent to the loggingsystem.

The base unit can also include an emergency monitor feature which iscode plug selectable. When a priorty alert packet is received, the baseuntil will go immediately into a priority mode and acknowledge themobile unit and terminate any retransmission sequence. The base operatormay then activate an emergency monitor sequence which will transmit adata packet to the mobile unit which enables the radio transmitter forten seconds. At the end of the ten seconds, the mobile will send anotherpriority alert packet. The base will continue to send an acknowledgepacket which will enable the transmitter. The cycle will continue untilthe operator at the base clears the emergency monitor feature with theclear key. Thus, the base operator can voice monitor the activity of themobile unit in the priority mode.

The base unit is capable of storing up to 64 mobile initiated inbounddata packets. Whenever inbound data packets are received and properlydecoded, the unit code and status information is placed in the memory.The method of storage is last in, first out, (LIFO) which is essentiallya stacking operation. As a new ID is received, it is placed at the topof the stack and the ID codes currently in the memory are pushed downthe stack. The operator may use a recall key to advance the stackpointer and display the next entry. A clear key is used to position thepointer at the stack top which displays the most recent ID and status.This feature is provided as a review mechanism in situations whereseveral data packets are received in quick succession to enable theoperator to keep track of all unit members.

The base unit also provides memory capability to queue up operatorstatus packets as they arrive in time, up to 128 operator status datapackets. The method of storage is essentially a queuing operation offirst in, first out (FIFO). If there are any data packets in the queue,the operator may display the next ID code and status and remove theprevious display. One of eight status indicators is used to show anactive or inactive queue. If the queue is active the operator may also,by pressing a clear key, display the first packet in the queue. Inaddition, a status queue control allows the terminal operator to enableor disable entries to the queue. Only operator status packets arequeued. PTT ID transmissions and priority alerts will be displayed whenthey occur but will not affect operation of the queue. If the queue isdisabled, any received operator status packets will be immediatelydisplayed or if the terminal contains a LIFO stack, it will be placed onthe LIFO stack. If the queue control is enabled, an operator statuspacket will be queued without affecting terminal operations includingthe display. However, a short beep will be heard to inform the operatorof an arriving status.

Polling of a limited number of mobile units for operator status andalternate status is provided by the base unit. This feature allows theoperator to scan the system and produce a status list of a select groupof mobile units. The operator may also select a particular status byentering a beginning unit number from the keyboard and then initiatingthe poll and entering a unique status where the poll is to stop. Thepoll will start at the entering number and sequentially interrogate themobile units for status. Each time the status packet is received, theunit will perform a match operation and if a match exists the poll willstop. If there is no match, however, the poll will continue until theupper ID limit is reached or the poll count, which is preprogrammed to adesired value, such as ten, is depleted.

All of the base units are equipped with control logic to preventsimultaneous channel access by multiple units connected in parallel. Thesame logic is used to inhibit inbound transmissions when the RF channelis busy. Each unit has a busy output and an inhibit input which arenormally connected together, forming a single coupled to the externalinterface 130, that becomes both a sense and a control line. Before anycommands are executed by the unit, the inhibit line is tested foractivity. If the line is clear, the command is transmitted and the unitasserts a high level on the busy line indicating use of the channel. Theline will remain busy until an acknowledge is received or theretransmission cycle is complete. If the channel is busy at the commandtime, the unit will wait until a line becomes clear and hold will bedisplayed indicating to the operator that the line is busy. When theinhibit line clears, the unit will not transmit immediately. Eachterminal in a multi terminal system contains a priority number from 0 to254 in its code plug. This number is used to generate a delayproportional to the priority number. The terminal will wait out thisdelay and then re-sample the inhibit line. If the line is still busy,the wait process will continue until access can be obtained. A randompacket delay cycle is also used in the delay process if a simple datacommand is being performed. If the line is clear, the unit transmits asdescribed above. The inhibit input line may be connected to the busyoutput line because each unit knows if it is busy or not. Thus, a simpletwisted pair is all that is needed to connect multiple terminals.Another feature involving multiple terminals in the same channel relatesto command overlap. Each and every command that is executed by aparticular unit will affect only that unit. If a unit interrogates aparticular mobile unit for status, for example, the status packet thatthe mobile returns will be displayed on that unit only and will notaffect other units on the channel. This feature allows independentcontrol by multiple operators but only applies to outbound commands. Anyinbound data such as operator status and priority alert will bedisplayed on all terminals on that channel. This may be defeated byusing the status matching technique or dynamic range selection discussedhereinabove or by simply defeating the particular receiver function viathe code plug.

A mode of selective voice calling (AUTO SEL CALL) is available on allbase units selectable by coding the code plug. This feature allows forsimple dispatching in a selective manner. The operator enters thedesired ID code, the system will wait for the microphone PTT switch tobe depressed. When it is, an unmute data packet will be transmittedsignalling the selected mobile units to unmute their receiver audio.When the PTT switch is released, a mute data packet is sent. During thisperiod of selective voice calling (AUTO SEL CALL) transmission, the baseunit display will read CALL, indicating to the operator that a SEL CALLis being made. By means of the keyboard, the AUTO SEL CALL mode may beenabled or disabled. If disabled, no selective call will be made whenthe microphone PTT switch is depressed. The logging system can recordboth SEL CALL and normal voice transmissions. If a mobile unit makes avoice transmission to the base, the unit ID code will be displayed onthe base unit. The base operator may simply press the microphone PTTswitch and talk. No other key entries are necessary and the mobile unitwill be selectively called.

Each time a command transmission is performed by the base operator, thereceiving mobile unit may send an acknowledge packet. If the decodeddata packets are correct indicating that the handshake is successful,the base unit will display an acknowledge indication that the mobilereceived the command. If the command happens to be an interrogation fordata, such as operator status, and the handshake is successful, then thedisplay will show the received data and no acknowledge will bedisplayed. If the handshake was not completed on the first transmission,the unit will automatically retransmit the command in a random fashionfor a number of times determined by the code plug unless an acknowledgepacket is received within this interval. An acknowledge will terminatethe sequence. If no acknowledge is received after the total number oftransmissions allowed have occured, the display will show a failindication and the operator may re-initiate the command. The base unitcode plug can be programmed so that the channel sense is used toautomatically monitor the channel before transmissions andre-transmissions. The same inhibit control line is used as that used formulti-terminal control. If the channel is busy, the data is inhibited.However, when the channel clears, a random clock will begin to samplethe channel for activity when the clock times out. If the channel isstill busy, the random cycle/sample process will continue. However, ifthe channel is clear, the command data packet will be sent to the mobileunit and an acknowledge will be received.

A closed loop signalling system test can be performed on selected mobileunits by all base units. The test performs a series of radio checkcommands which include mobile acknowledgement. It is normally used atsystem start up, but may also be used in system diagnostic tests. Whenthe operator enables the test mode, the terminal will prompt theoperator for the unit ID code of the mobile to be tested and the numberof individual tests to be performed (9,999 maximum). When the test iscompleted, the display will indicate the number of successful closedloop tests. The logging system will also be used to show all the datarelative to each individual series of tests. The results of the testwill reflect the statistics of the RF path mobile and base radios, etc.and may be used to correct any system problems.

An optional code plug module is available for the base unit to allowprogramming of mobile unit, group, and fleet ID codes, selective callingmuting modes and system delays. The system delay contained in the baseunit code plug is also automatically inserted for all mobile unitsregardless of shared or dedicated configurations. When the module isconnected to the base unit, the unit is automatically placed in theprogram mode. The programmer provides both a read and a program command.If the read command is executed, the terminal will display all relevantdata to the operator. Error control is provided to test the ID codes forproper values and inform the operator of an improper code plug. If theprogram command is executed, the terminal will prompt the operator forthe necessary data, attempt to program the code plug and than displaythe contents. Error control is also provided in the program mode toprevent the programming of invalid codes.

The base unit performs a limited diagnostic test of the hardware,software system on power. Real time clock, random access memory, codeplug, control ports and other various circuits are tested and any errorsare reported via the display system and the audio alert. Also, a commandkey is available to test the four digit display and the eight statusindicators.

Referring now to FIG. 5, there is shown a block diagram of a mobile unitcontrol circuit for use in conjunction with a mobile transceiver, thatmay be advantageously utilized with the present invention. The mobileunit of FIG. 5 consists primarily of a microcomputer 150 (e.g., MotorolaMC3870) and associated peripheral circuitry. The processor performs allof the PSK modulation, demodulation, encoding and decoding of thesignalling system. It also performs all control logic and managementfunctions of the mobile system.

Incoming data is applied from a receiver detector in analog form to thediscriminator input 186. It is then bandpass filtered by bandpass filter190 to remove unwanted signals and receiver noise. The signal is thenlimited through the limiter 192 and than processed by the MPU 150. Thecomputer performs coherent detection of the signal resulting in variousdata packets which provide the command and control information for theunit.

Data to be transmitted is prepared in data packets in the MPU 150 andpresented as PSK modulated packets at the output 178. The data packet isthen filtered using the same bandpass filter 190 as in the receivingmode to remove undesirable low frequency energy from the PSK data. Thesignal is than coupled to the microphone output 188 to the radiotransmitter. The microphone is muted during data transmissions toprevent any voice interference. All of the transmit control, audiomuting, tone generation and channel sensing is performed by the MPU 150.A code plug 152 is coupled as shown to the MPU 150 and contains all ofthe system information and selected options of the unit. The data in thecode plug 152 is read by the processor 150 and then used in the controlof operation of the unit. A watchdog timer 156 is coupled to the MPU 150to monitor a known signal out of the processor and reset the machine inthe event of processor failure or transient conditions. An emergencyswitch, 158, is coupled directly to the MPU 150 as shown as are a set ofeight status switches 162. A number of input and output switches andindicators, such as the horn and lights, are coupled to the MPU 150, viathe interface circuit 164 and the conductor 172, as shown. A data cycleoutput 160, a muting input and two tone outputs are also provided, asshown. The mobile unit system also requires a five volt power supply 170and a 9.6 volt power supply 168.

The unit, group, and fleet ID code of each unit are stored in the codeplug, as well as individual system functions such as ID, status,priority alert and select call.

A unique unit identification code is transmitted with every voicetransmission and is triggered off the microphone PTT switch which isinput to the MPU 150 at input 180 of FIG. 5. The system can beprogrammed so that the ID is sent at key-up or key-down or both or theID may also be message oriented where only a single transmission occursafter, for example, the removal of the microphone from the hang-up box.The transmission time of a mobile data packet is approximately 325milliseconds including the radio transmitter turn on delays. However, toallow for the variable system delays the mobile unit also generates,based on the code plug data, the transmission delay for the system. ThePTT ID transmission may also be programmed via the code plug to sendstart/end status with voice transmissions such that the base unit willprovide automatic voice unmuting and muting control, indication of anactive transmission and logging of transmission duration.

A very flexible status option can be programmed into the system via thecode plug which allows various arrangements of status and message toreside in the system. Two levels of status are available, operatorstatus and alternate status. The alternate status requires an optionalexternal interface card 154 of FIG. 5 which is coupled via an externalbus to the code plug 152.

There are three distinct types of operator status available in themobile unit; new operator status, current operator status and messages.New operator status requires a positive action by the mobile operator.This may be a change in status in which case the operator willphysically change a set of switch settings and send off the new statusto the base. The mobile unit may have up to nine switches which may bemomentary, push push type, interlocked or thumb wheel type switches,depending upon the requirements of the particular system. Currentoperator status always reflects the most recent setting of the statusswitches but does not require any action by the mobile operator. Thebase unit is capable of obtaining the current operator status of anymobile unit without any action by the mobile operator. And, in addition,current status can be automatically transferred to the base on every PTTID transmission. Messages are status of transient nature. To send amessage, the mobile operator must activate a switch and the base unitwill automatically display the message each time it is sent. However,the base unit is not capable of obtaining messages from a mobile unit,nor will any messages be sent along with voice transmissions. Newoperator status and message transmissions may be manually sent with theoperator monitoring the received channel before transmission or may beautomatically sent with the channel being sensed for traffic beforetransmit.

Manual status transmissions involve a sequence of simple operations.This type of status is used in systems where channel sensing isimpractical or impossible such as in radio systems where no radio signalis available for sensing channel activity. When the mobile operatordecides to transmit a status to the base unit he sets the proper statusswitches and the radio is automatically placed in the monitor mode. Hewaits for the channel to become clear if it is busy, then presses amomentary send switch at which point the data packet containing thestatus information will be transmitted immediately and the base unitwill acknowledge. Lock out is provided so that multiple sequences willnot occur if the send switch is not released.

With automatic status, no channel monitoring by the operator isnecessary since the channel is sensed for any ongoing traffic, data orvoice. If the channel is busy, the data transmission is inhibited untilthe channel clears, when a random clock will begin and the channel willbe sampled for activity when the clock times out. If the channel isstill busy, the random clock cycle will continue. If the channel isclear, the data packet containing the status will be transmitted to thebase unit and an acknowledge will be sent back to the mobile unit. Thisprevents overlap of several units pending transmission. The optionalautomatic monitor mode can be used in any status configuration. Messagesare sent in the same manner as operator status except momentary switchesare used.

There are three code plug selectable status/message transmission modesavailable in the mobile unit; single without acknowledge, single withacknowledge, and multiple with acknowledge. The single withoutacknowledge mode is intended for one way systems without receivingcapabilities. Each time a status or message transmission is initiated bythe mobile operator, the data packet is transmitted once and there is noacknowledge transmission by the base unit. This is a global modeapplicable to all options in the mobile unit. Thus, if no acknowledge isselected for the status mode, there will be no acknowledge for all datapackets. Since there is no acknowledge sent for data transactions therecan be no operator feedback of the successive transmission.

The single with acknowledge mode allows for all status and messagetransmissions to be acknowledged. If the handshake is successful, themobile unit will produce a short audio tone indicating that the statusor message was received at the base. If the handshake was not complete,meaning that the mobile did not receive the acknowledge, ano-acknowledge indicator will flash indicating to the mobile operator abad transmission sequence and permitting the operator to thenre-initiate another sequence. Thus, the mobile operator is given bothpositive feedback and negative feedback on status and messagetransmissions.

The multiple with acknowledge mode is identical to the single withacknowledge mode except retransmissions will automatically occur if theinitial transmission was unsuccessful. This is an extremely reliablemode of operation. Thus, if an acknowlege from the base unit is notreceived within a random time interval, the mobile unit willautomatically sense and re-transmit the status data packet. This processwill continue until an acknowledge is received or a programmed number ofretransmissions have occured. As in the single with acknowledge mode ashort audio tone will alert the mobile operator of a successfulsequence.

There are eight possible status switch inputs for a mobile unit. Acommon configuration would be a seven button status system where all ofthe seven status switches are mechanically interlocked. Each time astatus change is desired the operator pushes the desired switch whichwill lock into position and remove and previous setting. The status maybe automatically transmitted at that point or be initiated by a ninthswitch, the momentary send switch. To send the same status, the operatormust use the send switch independent of manual or automatictransmission. Many other configurations are possible including variousselect call switch combinations with status. The status system is alsocapable of supporting momentary message switches along with interlockingstatus switches. The message switch being momentary, will transmit atransient message. If a system involving more than one message switch isneeded, the mobile unit can have up to eight unique messages. Themessage switches are all momentary switches and the send switch istherefore unnecessary. A powerful feature of the mobile unit statussystem is that each of the status positions are independent.

Another important feature of the status system of the mobile unit ofFIG. 5 is the ability of the base unit operator to inform the mobileoperator to update his operator status. This is done by the use of acommand in the base unit which will cause the no-acknowledge indicatorto be activated at the mobile, signalling the mobile operator to updatehis operator status switches.

Alternate status is a general purpose status function providing analternative or extension to the operator status. Its operation isdifferent from operator status in that the mobile operator may notinitiate an alternate status transmission in the basic system. In asystem containing the priority alert option, the priority alert datatransmissions will also send the current alternate status. Since thealternate status is sent along with priority alert, the status may beused as location information, extended priority levels, vehicleswitches, etc. In these situations, the alternate status may beinitiated by the mobile unit. The alternate status option requires theoptional interface 154 of FIG. 5. The mobile code plug is removed fromthe mobile unit and inserted on the external interface 154. A ribboncable connector is placed between the code plug socket on the mobileunit and a similar socket on the interface card. The data and addressbus of the code plug is than multiplexed with alternate status. Sevenparallel inputs and seven independent parallel outputs are provided withthe alternate status option.

The base unit may interrogate any mobile unit for alternate status. Thebase is also capable of setting any combination of mobile alternatestatus outputs. The seven status inputs may be connected to switches asin operator status thereby providing extended status capability. In aconfiguration using seven status switches and seven message switches,the message switches are momentary and the status switches arepushbutton type or interlocked. When a message is transmitted, thestatus is not sent along. Instead, the base operator will manuallyinterrogate the mobile unit or the base unit can be programmed toautomatically retrieve the alternative status when a message isreceived. If the alternate status outputs are used as indicators in thesame system, the indicators may be used as base status. If alternatestatus is used to represent vehicle status, the seven inputs can beconnected to sensors in the vehicle, for example, oil pressure, fuel,temperature, etc.

The priority alert option is independent of the other options and may beenabled in any mobile system configuration. The priority alert isnormally to be activated by an external switch such as emergency switch158, FIG. 5. When activated, this normally closed switch will trigger asequence of special data packet transmissions that have absolutepriority over any other mobile unit functions. The initial priority datapacket is transmitted immediately regardless of any channel sensinglogic. If an acknowledge is not received within a random time interval,the mobile unit will automatically retransmit the priority data packet.A total of 20 transmissions will occur if an acknowledge is notreceived, in which case the operator may re-initiate another sequence. Asequence of transmissions will terminate immediately upon receiving anacknowledge. For security purposes, the mobile operator is not informedof positive or negative acknowledge. Activation of the Priority alertwill lock out all other data functions until an acknowledge is receivedor the sequence is terminated. When a priority alert is received by thebase unit, the display indicating the mobile unit number will flash andan alarm will sound. The base unit will transmit any one of two types ofacknowledge packets determined by the programming of the code plug. Thefirst type is a normal acknowledge which terminates the prioritysequence in the mobile unit. The second type is an emergency monitorpacket which will terminate the priority sequence in the mobile unit andthan will key up the radio transmitter for a fixed period of time (inthe preferred embodiment, 10 seconds). At the end of this time periodthe mobile unit will send another priority data packet to the base andthen switch to the receive mode. The base unit will continue to sendemergency monitor data packets in this cyclical fashion until a clearingoperation is performed by the base unit operator. This allows the baseoperator to voice monitor the activity of the mobile vehicle in theevent of a priority alert. The same emergency monitor data packet thatis used to enable the transmitter of a mobile unit in the priority alertmode is used to disable all other mobile transmitters in the systemequipped with the mobile unit control systems. This feature provides aclear-channel to the unit in the priority mode. In addition, if themobile unit has operator status, that status will be sent to the baseunit along with the priority condition, with the priority packetcontaining the operator status. If the mobile unit has alternate status,that status is also sent. With this feature, various levels of prioritymay be established within a system. In addition, the mobile unit willrespond to a unique command to initiate a priority alert sequence. Thiscommand may be issued by the base unit or by a portable transmitter,thus, allowing remote emergency systems where the mobile is used as arepeater.

A select call option is available with the mobile unit and is totallyindependent in operation and selection from other features. The purposeof the select call system is to allow private and/or secure voicecommunications and paging operations. Selective voice calling isaccomplished in the mobile unit by muting and unmuting the mobile radioaudio. These operations are controlled by various data packets thatoriginate from the mobile and base units. The base unit is capable ofsupporting several simultaneous modes of voice calling.

An auto select call mode of operation is provided whereby the base unitoperator simply enters the unit, group or fleet identification code onthe terminal and uses the microphone as normal. The selected unit,group, or fleet of mobile units will automatically unmute the audio forthe duration of the voice transmission and then re-mute. The auto selcall mode does not provide acknowledge due to the fact that the voicefollows the unmute data packet while holding the transmitter key. Thesystem is automatic in that the base operator is not required to press acall switch for each transmission.

A basic switch configuration for a select call mobile unit would includea call light used in voice calling and paging to indicate that the baseunit has signalled that unit, except in the AUTO SEL CALL mode where thecall light would not be affected. A reset switch, which would be amomentary type switch, can be provided to clear the call light andremute the audio if the automatic muting fails. A horn and light switchare provided which are push-push type switches and are used to engagethe horn and lights for external alarms. A base group, and fleet switchmay be provided to permit encoding capability to the mobile unit and arepart of the AUTO SEL CALL mode. The switches are preferably mechanicallyinterlocked. With these three switches, the mobile operator mayselectively voice call the base, other members of his current group, orhis fleet. If the base switch is selected, all voice transmissions fromthat unit will be directed to the base unit. The base unit will displaythe unit identification code as in the PTT ID option and no other mobileunits in the system will hear the transmission. If the group switch isselected, all voice transmissions from that unit will be heard only bymembers of the same group. The base unit will display the groupidentification code and no other mobile units in the system will hearthe transmission. If the fleet switch is selected, all voicetransmissions from that unit will be heard by members of the same fleetand the base unit will display the fleet identification code. With thegroup or fleet switch selected, a voice transmission by the mobileoperator will display the group or fleet ID code at the base unit.However, the mobile unit code plug may be programmed so thatconcatenated data packets are sent at the end of every group or fleetvoice transmission to permit the base unit to display the unit code ofthe transmitting mobile. With this feature programmed into the codeplug, the base unit will sequentially display the group or fleet codefollowed by the unit code. A call with acknowledge mode of voice callingis available to the base unit operator who would enter the unit, group,or fleet identiication code of the units to be called. He then wouldpress a call switch and a responding mobile unit will unmute the radioaudio, light the call lamp and activate any external alarms provided,alert the mobile operator with a short audio tone and send anacknowledge packet to the base. No acknowledge packet would be commandis issued to a group or a fleet. This mode does not provide automaticremuting of the audio. The mobile operator must manually reset themuting by pressing a reset switch, by coming offhook, or by initiating avoice transmission.

When the select call option of the mobile unit is used in a private linesystem, there are three major muting modes available: AND, OR, and none.With DPL or PL muting used in the system and the mobile unit in the ANDmuting mode, both the proper PL or DPL code and the correctidentification code must be present to unmute the receiver audio. Whenthe microphone is removed from the hangup box or the monitor operateswitch is placed in the monitor position, all muting is disabled. If,however, an individual or group calling is desired from base to mobilewithout disturbing other mobiles in the system while retaining a PLoperation for general mobile to mobile and mobile to basecommunications, muting may be selected as an OR mode. In the OR mode,the audio will respond to either a select call or a proper PL or DPLcode. If the system is to be used for external alarms and call lightoperation and all units are to hear all transmissions with the proper PLor DPL code, then no muting is selected.

There are two paging modes available to the base operator for which themobile unit can respond. The first paging mode simply alerts the mobileoperator with a series of audio tones, activates any external alarms orenables the call lamp. No audio muting or unmuting is performed. Thebase operator enters the unit, group, or fleet identification code ofthe units to be paged. He then presses a page switch and the addressedmobile unit will perform the above action and transmit on-acknowledgeback to the base. Group and fleet page operations will not beacknowledged. A second paging mode is identical in operation to thefirst except that no audio tones will be produced.

All mobile units provide for group reassignment by a base unit operator.The base operator may interrogate any unit for its current goupidentification code and may also dynamically change that code. Since thegroup code may be dynamically altered, the group code may be used insome systems as a variable identification code. Once a mobile unit groupID has been changed, any group addressing of that unit will performed bythe new ID number. When a mobile unit is powered up, the group IDcontained in the unit code plug is placed in random access memory. Thebase unit may alter this code in RAM by use of a re-grouping command.The mobile unit will always use the current group code in RAM for groupoperations.

All mobile units are provided with a "radio check" function. This isactivated by the base operator entering the unit ID code of the mobileto be checked followed by a radio check command. The mobile unit willthan respond with a normal acknowledge. This feature may be used insystem diagnostics or to test the availability of the mobile operator.

A part of the select call feature permits the base unit to selectivelyenable or disable voice transmission control of mobile units. The baseoperator may enter the unit group or fleet identification code of theunit to be enabled or disabled. He than executes the disable command andthe selected unit or units will be inhibited from further voicetransmissions. The command has no effect on data transmissions.

The optional external interface, 154, provides all the logic andinterfacing to enable the alternate status feature and data channelselection logic. The data channel selection logic will enable a mobileunit to transmit any and all data on specific designated channels. Itdoes this by way of the frequency selection switch of the mobile controlhead. An audio alert mechanism is provided to alert the operator of aninvalid channel selection if any data transmissions are initiated on aninvalid channel. The logic may be capable of automatically reverting toa selected data channel.

FIG. 6 is a flow diagram of the RESTART routine of the base unitcomputer program for the microcomputer 100 of FIG. 4 for implementingthe invention. The program is entered at block 200 upon power up andinitialization occurs as illustrated at 202. The RAM, clock, ports, andcode plug are tested at 204 and if an error is detected, an error codeis displayed, as illustrated at 206, after which the system waits forrestart to be initiated by the operator as indicated at 208. If no erroris detected, the routine continues instead to block 210 displaying astart message on the display 98 and proceeds to 212 to test for thepresence of the programmer module. If the programmer module optionexists the program flow proceeds to block 214 and then to the PROMPROGRAMMER HANDLER routine. If no PROM programmer option exists, thenthe routine proceeds to blocks 216 and 218 to activate the printer toprint a predetermined herald and log on information. The routine thentransfers control to the PSK RECEIVE routine.

A flow diagram of the PSK RECEIVE routine is shown in FIG. 7, whichshows entry to the routine at block 230. The PSK demodulator isimmediately entered at 232. The PSK demodulator is a separate routinefor demodulation and detection of the PSK modulated signal such as thatdescribed in a co-pending application filed by Timothy Burke and ScottNoble on Dec. 7, 1981, bearing serial number 328,332 and assigned toMotorola Inc. If a keyboard interrupt is generated, the program flowproceeds as indicated at block 234 to the KEYBOARD HANDLER routine shownat 236. Otherwise, the routine will proceed to block 238 to test for theexistence of the PROM module which, if present, causes the program flowto proceed to block 240 to the PROM programmer. If not, the program flowproceeds to block 242 to test the push-to-talk (PTT) transmit switch. Ifthe push to talk transmit switch is activated, the program flow proceedsto the TRANSMIT HANDLER routine as indicated at 244 and if notactivated, program flow proceeds to block 246 to test timed vectoring.If the result of the test at 246 is positive, program flow proceeds toblock 248 to get the exit vector and then to 250 to the vectoredroutine, otherwise, program flow will proceed, as shown, to block 252 todetermine whether there has been a 112 bits detected, indicating acomplete data packet. If there are not 112 bits program flow willproceed to block 254 and return to the PSK RECEIVE at block 230. If the112 bits have been detected, program flow proceeds to block 256 to theconvolutional decoder for decoding of the 112 bit encoded signal andthen to block 258 where the cyclic redundancy check code is computed andto 260 where the computed CRC is compared with the detected CRC. If theresults of the CRC check is negative, then program flow proceeds fromblock 262 to 264 to the beginning of the PSK RECEIVE routine at 230. Ifthe CRC check is positive, the program flow proceeds as shown at 266 tothe PACKET PARSING routine.

The PACKET PARSING routine is entered at block 270 of FIG. 8A andprogram flow proceeds to block 272 to test the bounds of the ID address.If the address is outside of the bounds, then program flow proceeds, asshown, at 274 back to the PSK RECEIVE routine. However, if the IDaddress is within the predetermined bounds stored in memory, thenprogram flow will proceed to block 276 where the program will test for avalid operational code (OP code) and if the code is not valid, theroutine will return to the PSK RECEIVE routine as indicated at 278. Ifthe operational code is valid, than the program proceeds to block 280where the program will proceed to the proper mode as determined by theoperational code. If the OP code addresses a select call mode theprogram flow proceeds to block 282 and then, as indicated at 284, theprogram is transferred to the PSK RECEIVE routine. If a priority alertmode is addressed by the OP code then the program will proceed to block286 where the priority alert function is activated and as indicated at288, the status key match test is performed. If there is not a match ofthe status key, then the program proceeds to the PSK RECEIVE routine asindicated at 290 and if the status key matches, then as indicated in292, the priority alert function is performed and the routine thanproceeds to transfer control back to the PSK RECEIVE routine asindicated at 294. An acknowledge OP code will cause the program toproceed to block 296 for execution of the acknowledge function. Programflow will proceed to 298 where the program will test to determine if itis waiting for an acknowledge and if not, then the routine immediatelyproceeds to transfer to the PSK RECEIVE routine as indicated at 300,however, if it is waiting for an acknowledge then the program proceedsto block 302. At block 302 acknowledge functions are performed andcontrol in the transferred to the PSK RECEIVE routine as indicated at304. A current group OP code will cause program flow to proceed to 306and as indicated at 308 a test for waiting is again performed and if nowait, than program flow is transferred directly the PSK RECEIVE routineas indicated at 310. Otherwise, program flow proceeds to block 312 whichperorms the group functions and then transfers control to the PSKRECEIVE routine as indicated at 314. The PACKET PARSING routinecontinues from FIG. 8A to FIG. 8B at 316. FIG. 8B, indicates at 318 thatif a PTT ID function is addressed by the OP code than program flow willproceed from 318 to 320 to stop polling if polling is occuring and thento block 322 to test the status key for a match. If no match exists, theprogram flow proceeds immediately to the PSK RECEIVE routine asindicated at 324 and if a match occurs, then at 326 the ID functions areperformed and then the program transfers to the PSK RECEIVE routine asindicated at 328. If an alternate status function is addressed by the OPcode, then the program proceeds to block 330 and then to 332 to test ifthe program is waiting and if no waiting is occuring, than the programproceeds directly to the PSK RECEIVE routine as indicated at 334 andotherwise proceeds to block 336 to test if a poll is in progress. If apoll is in progress, then the program proceeds to the POLL EXIT routineas indicated at 338 and otherwise proceeds to block 340 to perform thealternate status function and from that point the program control istransferred to the PSK RECEIVE routine as indicated at 342. If the OPcode addresses a current operator status function, program flow proceedsdirectly to block 344 and from there to block 346 to test to determineif the program is waiting. If no waiting is occuring then the programproceeds to the PSK RECEIVE routine as indicated at 348 and otherwiseproceeds to block 350 to test to determine if a poll is in progress. Ifa poll is in progress, the program flow is transferred to the POLL EXITroutine as indicated at 352 and otherwise proceeds to block 354 toperform the current operator status function and then transfers programcontrol back to the PSK RECEIVE routine as indicated at 356. Finally, anOP code calling for a new operator status function (or message) willtransfer control directly to block 358 and then to block 360 where thepoll is stopped, if polling is occuring. Program flow then proceeds toblock 362 where the status key is tested for a match. If there is nostatus match, then program flow is transferred to the PSK RECEIVEroutine as indicated at 368 and if a match occurs, then the new operatorstatus function is performed as indicated at 366 after which the programcontrol is transferred to the PSK RECEIVE routine as indicated at 364.

The KEYBOARD HANDLER routine is illustrated in FIGS. 9A, 9B and 9C andis entered by means of a keyboard interrupt as indicated at block 370.The KEYBOARD HANDLER routine at 372, immediately proceeds to get the keywhich was activiated as indicated at 374 and proceeds to test for thePROM programmer at 376. If yes, then program flow proceeds to returnfrom the interrupt as indicated at 382. In addition, program flowproceeds from 396 if the result is negative at 378 to test for clockinitiation, and if that is positive, the program flow proceeds, again,to return from the interrupt as indicated at 382. If the result of thetest at 378 is negative, the program flow proceeds to 380 where the"system-test" function as examined. If the result is positive, again,program control returns from interrupt as indicated at 382 and otherwiseproceeds to block 384 to determine the key activated, as indicated atblock 384. At block 386, the clear key is tested and if positive, thedisplay is cleared as indicated at 388 and program control istransferred to the PSK RECEIVE routine as indicated at 390. Otherwise,program flow proceeds to block 392. At this point, a display pendingtest is performed and if positive, program control is transferred to PSKRECEIVE routine as indicated at 394, and otherwise proceeds to block 396to test if a PTT command is in progress. If positive, the routinereturns to the PSK RECEIVE routine, as indicated at 398 and otherwiseproceeds to block 400 to determine if a poll is in progress. If a pollis in progress, the routine transfers control to the PSK RECEIVE routineas indicated at block 402 and otherwise program flow proceeds to block404 and from there to block 406 as indicated in FIG. 9B. At block 406,the program tests to see if a "system-test" is in progress and if theresult is positive, the program flow is transferred to the PSK RECEIVEroutine as indicated at 408 and otherwise program proceeds to block 410.At 410, the program tests as indicated for a priority alert in progressand if the result is positive, the program flow proceeds to block 412 totest to determine if a function key had been activated. If the result isnegative, the program flow is transferred to the PSK RECEIVE routine asindicated at 414 and if positive, the program flow proceeds to block416. At block 416, the program tests for the emergency monitor option,if the result is negative the program control is transferred to the PSKRECEIVE routine as indicated at 418 and otherwise proceeds to block 420where a test for the second function key is performed (two function keysare required to activate an emerging monitor command). If the result isnegative, program proceeds to block 422 where the emergency monitorcount is incremented and then to the PSK RECEIVE routine as indicated at424. If the result of the test at 420 is positive, the program proceedsto the emergency monitor transmit, transmitting the emergency monitorpacket as indicated at 426. If at block 410, the priority in progresstest is negative, program flow proceeds directly to block 428 where theprogram test of the terminal is waiting for an acknowledge packet. Ifthe terminal is waiting, the program proceeds to the PSK RECEIVE routineas indicated at 430 and otherwise, as indicated at 432, proceeds toblock 434 shown in FIG. 9C. At block 434, the program tests for acommand-in-progress, and if there is a command-in-progress, the programnow proceeds to 448 where the test for a function key (which is used forcommand execution), is performed. If the result of the test is negative,program flow is transferred directly to the PSK RECEIVE routine asindicated at 450 and otherwise proceeds to block 452 to determine if thesystem is waiting to poll. If the result is positive, the program flowproceeds to block 454 to transmit the start of the polling sequence, andotherwise proceeds to block 456 to determine if a "system test" is inprogress. If a "system test" command exists, then program flow proceedsto block 458 causing a "system test" initiation, and otherwise proceedsto a normal command transmit as indicated at block 460. If at block 434,the command in progress test is negative, program flow will proceed toblock 436 and test for a pending function. If the result is positive,the program test for control vectoring is indicated at 438 and if theresult is positive, the program fetches the vector as indicated at 440and than exits to the vectored address as indicated at 442. Otherwise,at block 438, program flow proceeds to block 444 to translate theactivated key to a command vector and then exits the program through thecommand vector as indicated at 446. If at 436, the function pending testis negative, program flow will proceed to block 462 where the key istested for a function key and if positive, the program will set thefunction pending flag as indicated at 464. The function will bedisplayed at 466 and then the program flow returns to the PSK RECEIVEroutine as indicated at 468. If the result of the test at 462 isnegative, program flow will proceed to block 470 where the displaybuffer will be obtained (since, at this point, the key is a numericentry) and a new key will be rotated in the display buffer as indicatedat 474. The program proceeds to 476 to test for a 3 digit sahred-systemconfiguration and if the three digit mode is present, the program flowproceeds to 478 to move the code into the fleet code display buffer, to480 to mask the most significant digit from the display buffer, and thento block 482 to clear pending flags. Program flow then proceeds to 484where the display is updated and then transfers program control to thePSK RECEIVE routine as indicated at 486.

FIGS. 10A, 10B and 10C show a flow diagram of the COMMAND routine forthe base unit computer program and as indicated at 492 is entered via acommand vector at 490. From the entry point 490 the program flow thenproceeds as indicated to one of several possible command modes. If thecommand is a group mode command, program flow proceeds to the group modeselect at 494 and obtains the display buffer as indicated at 496. Theprogram flow then proceeds to 498 where the display buffer is tested forvalid group and if the result is negative, performs a error exit asindicated at 500. Otherwise group mode is set as indicated at 502 andprogram flow proceeds to the PSK RECEIVE routine as indicated at 504. Ifa fleet select mode is called for, the program flow proceeds directly to506 and then to block 508 to obtain the buffer display and then to block510 to test for a valid fleet code. If the results of the test arenegative, the program makes an error exit as indicated at 512 andotherwise proceeds to block 514 to set the fleet mode and then transfersprogram control to the PSK RECEIVE routine as indicated at 516. Atransmit command will cause the program control to proceed directly toblock 518 and from there to 520 where the display buffer is obtained andtested for valid ID as indicated at 522. If the results of the test arenegative, an error exit is executed as indicated at 524 and otherwiseprogram flow proceeds to block 526 to get any auxiliary data. Theprogram then proceeds to block 528 to obtain the command code to 530 tomerge the OP code and data, and then proceeds to store the result in atransmit packet buffer as indicated at 532. The system flags are set orcleared as required as indicated at 534 and the PL or DPL and the audiomuting are disabled as indicated at 536. The command logo is thendisplayed on the display as indicated at 538 and the program flowproceeds to the PSK RECEIVE routine as indicated at 540 (awaitingcommand execution).

The command subroutine continues from FIG. 10A to FIG. 10B as indicatedat block 542. If a recall or a next in queue command occurs, the programflow proceeds to 546 to get the next memory address as indicated byblock 544 and 548. Once the next memory address has been obtained, theprogram proceeds to 550 to test for end of memory. If the result isnegative, the program proceeds to block 554 to display the stack orqueue position, and then to 556 to get a return address. Program flowthen proceeds to block 558 for time vectoring and then exits to the PSKRECEIVE routine as indicated at 560. If the result of the test at 550 ispositive, the program causes none to be displayed as indicated at 552and proceeds, as shown, to block 566. Block 566 may also be entered by avector return as indicated at 562 following a display of the unit IDindicated at 564. In addition, the block 566 may be entered as a resultof a first in, first out queue control toggle command as indicated at578 which results in toggling of the control flag as indicated at 580and a display of the flag state as indicated at 582 followed by transferto block 566 to get a return address. Program flow then proceeds toblock 568 for timed vectoring and then transfers program control to thePSK RECEIVE routine as indicated at 570. The command routine iscontinued in FIG. 10C as indicated by block 584, where if a secondarycommand occurs, entry is at 586 and the program proceeds to display FNC2 as indicated at 588 and then sets the keyboard vector flags asindicated at block 590. Then the return address is obtained at 592 andwaits for the key entry by way of an untimed vector at 594. Once the keyentry has occured, program flow is transferred to the PSK RECEIVEroutine as indicated at 596. Block 598 is entered via vector return andprogram flow proceeds to block 600 to get the entered key value andtranslate and then proceeds to block 602 to vector to the secondarycommand and than to 604 to perform the secondary command or functionrequired. Program flow is then transferred to the PSK RECEIVE routine asindicated at 608.

A flow diagram of the command transmit routine for the base unitcomputer program is illustrated in FIGS. 11A and 11B. The program isentered at 610 and proceeds to block 612 when the audio and PL or DPLare disabled. The program flow then proceeds to a system test todetermine if it is busy as indicated at 614 and if the result ispositive, the program displays "hold" on the display as indicated at 616and then computes a random delay at 618 and waits for the busy to clearas indicated at 620. The program flow continues to block 622 to get abusy return address and then to 624 for timed vectoring and proceeds totransfer program control to the PSK RECEIVE routine as indicated at 626.If the result of the test at block 614 is negative, the program flowadvances to block 628 to set the busy line and the display. The programflow then proceeds to block 630 disabling the keyboard and enabling thetransmit line and waits for the preprogrammed system delay as indicatedat 632. The program flow then continues to block 640 where the TRANSMITsub-routine is called and then to 642 to log the transmission on theprinter and clear the busy line. A test for polling is then performed atblock 644 and if the result is negative, a test for acknowledge isperformed as indicated at 646. If the result of that test is negative,program flow proceeds to block 648 clearing the transmit flags and thenas indicated by block 660 and 668 of FIG. 11B program flow istransferred to the PSK RECEIVE routine. If, however, the result of thetest for acknowledge at block 646 is positive, program flow proceeds toblock 650 to test if this is the first transmission. It should also benoted that if the test at 644 is positive, the program flow proceeds toblock 650. If the result of the test at block 650 is negative, programflow advances to block 654 and decrements a retransmission count andthen sets the system flags as indicated at 656. If the result of thetest at block 650 is positive, the retransmission count will be presetas indicated at 652. Program flow will then proceed to block 656 to setthe system flags and from there to block 662 as indicated by block 658.A random packet delay is computed at block 662 and then the returnaddress is obtained as indicated at 664. Program flow then continues toblock 666 for timed vectoring and to block 668 where the program controlis transferred to the PSK RECEIVE routine.

FIG. 12 illustrates a flow diagram of the RETRANSMISSION routine of thebase unit computer program. The RETRANSMISSION routine is entered at 670where the return address is obtained and proceeds to block 672 to testfor the retransmission count equaling zero. If it is not zero, theprogram control advances to 674 where the retransmission count isdecremented and program flow is then transferred to the COMMAND TRANSMITroutine as indicated at 676. If, however, the result of the test at 672is positive, program control is transferred to block 678 where theno-acknowledge flag and system flags are set and to block 680 where the"fail" indication is displayed. The program flow continues to block 682where the no acknowledge is logged on the printer and the programproceeds to block 684 to test to see if a poll is in progress. If theresult is negative, program flow is transferred proceeds to the PSKRECEIVE routine as indicated at 690. If the result of the test at 684 ispositive, the poll count is advanced as indicated at 686 and an exit tothe POLL EXIT routine is executed as indicated at 688.

A flow diagram of the POLL EXIT routine for the base unit computerprogram is shown in FIG. 13. The POLL EXIT routine is entered, as shown,at 692 and program flow immediately proceeds to block 694 where the pollcount is tested to determine if it is equal to the preprogrammed maximumvalue. If the result is positive, the poll is stopped as indicated at696 and program control is transferred to the PSK RECEIVE routine asindicated at 698. If the result of the poll test at 694 is negative, theprogram flow continues to block 700 and advances the poll ID number andthen proceeds to block 702 to set up the data packet and to 704 to setthe system flags. The program flow then proceeds to block 706 or timedvectoring and exits to the COMMAND TRANSMIT routine as indicated at 708.

The DATA TRANSMIT sub-routine flow diagram is shown in FIG. 14 and asindicated, the sub-routine is entered at block 710. The program flowproceeds immediately to block 712 where the 32 bit data packet isobtained and then the CRC code is computed at block 714. The data packetis then encoded into the transmit buffer as indicated at 716. Theprogram flow then proceeds to block 718 where the preamble code and synccode are obtained and appended to the transmit buffer as indicated atblock 720. The entire data packet is transmitted by the transmitterusing PSK modulation as indicated at 722 and the program control returnsfrom the sub-routine as indicated at 724.

FIG. 15 shows a flow diagram of the PROM PROGRAMMER HANDLER routine forthe base unit computer program. The PROM PROGRAMMER HANDLER routine isentered, as shown, at 730 and program control proceeds immediately to732 to test for the indicated option. If the result is negative, anerror exit is executed as indicated at 734, and if the result of thetest is positive, the program flow advances to block 736 to get thekeyboard key. Program flow then proceeds to block 738 where a test isperformed to determine if the programmer is connected and if the resultis negative, the program control is transferred to the PSK RECEIVEroutine as indicated at 740. If the result is positive, however, programcontrol continues to 742 where the key is tested to determine if it wasa clear key. If the result is positive, the display is cleared asindicated at 744 and the program control transfers back to block 736.If, however, the result of the test at 742 is negative, program flowwill proceed to block 746 where the key is tested to determine if it isa function key. If the result is that it is a function key, the programflow advances to block 748 where the function mode is set and to 750where the FNC 3 indication is displayed. Program flow is then transferedback to 736. If the result of the function key test is negative, theprogram then proceeds to block 752 to test to determine whether the oneor three key was activated. If the result is negative, an errorindication is displayed as indicated at 754 and the program flow istransferred back to block 736, as shown. If the result of the test at752 is positive a test to determine if the one key has been activated isperformed at 756 and if the result is negative (meaning the three keyway pressed) the code plug is programmed as indicated at 758 and theprogram flow proceeds to block 760 to read and display the code plug. Ifthe result of the test at 756 is positive, the code plug is read asindicated at 760 and the program flow then proceeds back to block 736.

Referring now to FIG. 16, there is shown a flow diagram of the STARTroutine of the mobile unit computer program. It should be immediatelynoted that the START routine can be entered at four entry pointsindicated as START at block 780, PSKREC at block 784, PSK at block 788and MAIN at block 792. Entering the START routine at block 780 theprogram flow proceeds directly to 782 where the ports and external busare cleared and the code plug is read. At this point, the PSK REC entrypoint at 784 permits entry to block 786 where program flow proceeds toset up the necessary muting. After block 786, the entry point PSKindicated at 788 permits entry to the next flow position at 790 whichsets up the PSK RECEIVER and the START interrupts. Program flow thenproceeds to block 794 which can also be entered from the MAIN entrypoint indicated at 792, where the channel monitoring is performedutilizing the PSK RECEIVE routine. Program flow continues to block 796where the PTT switch is checked to determine if it is on, and if theresult is positive, the program exits to the EXT routine as indicated at798. If the test at 796 is negative, the program flow advances to block800 where the program tests for a switch change and causes the programcontrol to transfer to either the TRANS routine, the EMERG routine theP1CHK routine, or the HUBCHK routine, determined by which type of switchchange occured, as indicated at block 802. If the test shows that noswitch change has occured the time out timer is checked to see if it hastimed out, as indicated at 804, and if the result is positive, programcontrol is transferred to the TIMCHK routine as indicated at 806. Iftime out has not occured, then program flow proceeds to 808 where a testfor word sync is performed. If word sync exists, than program flowproceeds to block 812 where phase ambiguity is corrected in a databuffer. Program flow will then continue to block 814 where the receiveddata word is checked to determine if the full 112 bits have beenreceived, and if the result is negative, program flow proceeds to block820 where the data operated squelch provides muting. In addition, if thetest result at block 808 was negative, program flow would proceed toblock 800 where a data operated squelch (such as that described in acopending application filed Dec. 7, 1981 by Scott Noble with serialnumber 328,359 and assigned to Motorola, Inc.) tests for presence ofdata and if data is detected then program flow proceeds to block 820 towill mute the audio and transfer control back to block 792 which is theMAIN entry point to the routine. If the result of the test at 810 isnegative, program flow will proceed directly to block 792 and thendirectly to block 794, as shown. A positive result in the test of block814 will result in program flow being directed to block 822 to thedecode section of the routine. Program flow then advances directly toblock 824 where all interrupts are disabled and the 112 bit data isdecoded. The program flow then proceeds to 826 where a cyclicalredundancy check determines the validity of the data. And if the resultis negative, program control is transferred from block 827 to the PSKinput of the routine at 788. If the result of the test at 826 ispositive, the program flow continues to 828 where a test is made todetermine if the system is in the emergency mode. If yes, program flowproceeds to block 830 where a check is made for the emergency monitor OPcode. If the result is positive, the program control is transferred tothe EMRMON routine as indicated at 834 and otherwise to the PSK input ofthe routine as indicated at 832. If the result of the check at block 826is negative, program flow transfers to block 836 where the ID address ischecked for validity, and a negative result causes the program flow tobe transferred to the PSK input of the routine, as indicated at block838. If the result of the test at 836 is positive, the program flowproceeds to block 840 where a check is made of the OP code and argumentagainst the code plug to verify that the unit has been programmed tohandle the option indicated. At block 842, the program checks todetermine if the function indicated is possible, and if the result isnegative, the program flow is directed to the PSK input of the routineas indicated at 844. If the result is positive, program control proceedsto block 846 where the function is performed and need for dataacknowledge checked, as shown in block 848. If the result is negative atblock 848, program flow advances to block 852 where program control willbe transferred either to the PSK or the PSK REC input of the routinedepending upon muting, as indicated. If the result of the test at 848 ispositive, a quarter second wait will occur before a transmission ofacknowledge or data back to the base, as shown at 850.

FIG. 17 shows a flow diagram of the EXT routine of the mobile unitcomputer program and is entered as shown at 854. Program flow proceedsdirectly to 856 where the interrupts are disabled and the code plug isread and then at 858 the program tests the code plug data to determineif the unit has PTT control. If the result is positive, program flowproceeds to 860 where the PTT is turned on and to block 862. If theresult of the test at 858 is negative, the program flow advancesdirectly to block 862 where approximately a 36 millisecond wait occursto permit a check of the data inhibit line. The data inhibit line isthen checked as indicated at 864 and if the result is positive, programflow is transfered to block 882 as shown where the program waits for aPTT signal for 180 milliseconds while the receiver is muted. If,however, the result of the check at block 864 is negative, a check forthe talk around option will be made as shown at block 870. If the resultof the test at 870 is negative, program flow will proceed to block 868and 872 where the PTT one shot will be checked to determine if it is setand if the result is positive, the program flow will proceed to block882 as shown. If the result is negative, the program flow will proceedto block 874 where the code plug will be tested to determine if a PTT IDis to be generated at the beginning, and if the result is positive, thenthe necessary status switches are obtained and the system delay isstarted following which the ID is sent at the beginning of thetransmission, as indicated at 876. Program flow will then continue toblock 878 where the code plug is checked to determine if a PTT ID is tobe sent at the end of the transmission. In addition, if the result atblock 874 is negative, program flow will proceed to block 878 and if theresult of the test at block 878 is positive, the switch values will bedetermined and the system will wait for the PTT switch to be deactivatedand an end of transmission ID will be sent as indicated at 880. Programflow will then advance, as shown, to block 882 after which the programflow will return to the PSK REC input of the START routine. If theresult of the test at block 870 is positive, the base, group, and fleetID's and switches are checked and system delay is added in at 880.Followed by sending of the packet and a wait for an end of transmissionsignal from the PTT. Program flow then proceeds to block 890 where themute packet is sent with no system delay followed by a test for group orfleet call as indicated at 892. If the result at 892 is negative,program flow will advance directly to block 882 as indicated, and if theresult is positive, program flow will transfer to block 878 to determineif an end of transmission ID should be sent. The program flow is thentransfered from block 882 to the PSK REC entry point of the STARTroutine as indicated at 884.

A flow diagram of the TRANS/EMERG routine of the mobile unit computerprogram is shown in FIG. 18. This routine can be entered at four pointsindicated as TRANS at 894, EMERG at 924, RETRAN at 904, and EMREPT at932. Entering the program at TRANS indicated at 894 program flowproceeds directly to block 896 where the interrupts are disabled and thecode plug data is read whereupon a test is made to determine whether thestatus option is allowed as indicated at 898. If the result is negative,the program flow transfers to the PSK input of the START routine asindicated at 900 and if the result is positive, the program flowadvances to 902. At 902, the data cycle is started wherein a low is puton the data cycle line to indicate status is being sent and thetransmission count is set or a wait period is established to allowchannel scan. Subsequently, program flow will proceed to block 906,however, block 906 can be entered from block 904 the RETRAN entry point.At block 906 the count is tested to determine if it is equal to zero andif the result is positive, the no acknowledge light will be activated asindicated at 908 and program flow will transfer to the PSKREC input ofthe START routine as indicated at 910. If the result of the test at 906is negative, a random time out period is fetched as indicated at 912followed by a test of the data inhibit line at 914. If the data inhibitline is on, the program flow will be transfered to the PSK input of theSTART routine as indicated at 916 and if the line in not on, the statuspacket will be set up as indicated at block 918. Program flow will thencontinue to block 920 where the count will be decremented and the packettransmitted and the program flow will be transferred to the PSK RECinput of the START routine as indicated at 922. If however, the routineis entered at the EMERG entry point indicated at 924, program flowproceeds directly to block 926 where the interrupts are disabled and thecode plug is read. The program then continues to block 928 where thepriority mode is started followed by starting the data cycle and settingthe transmission count in establishing the required wait period asindicated at 930. Program flow then advances to block 934 however, thispoint of the program can be entered at the entry point EMREPT asindicated at 932. At block 934, the count will be tested to determine ifit is equal to zero and if it is, the priority mode will be stopped, asindicated at 936, and program flow will be transferred to the PSK RECinput of the START routine as indicated at 910. If the count is notequal to zero, program flow will advance to block 938 where the randomtime out period is fetched followed by set up of the priority packet asindicated at 940. Program flow will then proceed to block 920 where thecount will be decremented and the packet transmitted followed by atransfer of program control to the PSK REC input of the START routine asindicated at 922.

Referring now to FIG. 19, there is shown a flow diagram of theP1CHK/HUBCHK routine of the mobile unit computer program. This routinemay be entered at two points; the P1CHK entry point indicated at 942 andthe HUBCHK entry point indicated at 966. If the routine is entered at942, program flow will proceed directly to blocks 944 and 946 where theswitch will be tested to determine if it has changed from a zero to aone. If the result of the test of the switch at 946 is negative, theprogram flow will transfer to the MAIN input of the START routine asindicated at 948, and if the result of the test is positive, the programflow will advance to block 950 where the interrupts will be disabled andthe code plug will read. Program flow will then continue to block 952where the call reset switch will be checked to determine if it is on. Ifthe call reset switch is on, relays and call lights will be cleared asindicated at 974 and the program control will then be transferred to thePSK REC input of the START routine as indicated at 976. If, however, theresult of the test at 952 is negative, program flow will proceed toblock 954 and 956 where the status switches will be checked to determineif there has been a change. If no change has occured, program flow willtransfer, as indicated, to 964 and if the result is positive, theprogram will continue to block 958 where a test is made to determine ifthe auto status option is available. If the result is positive, programcontrol is transferred to the TRANS routine as indicated at 960. If theresult of the test at 958 is negative, program control proceeds to block962 where muting will be opened to permit channel monitoring. Programflow will then be transferred to the PSK input of the START routine asindicated at 964. If the routine is entered at the HUBCHK entry pointindicated at 966, program flow proceeds directly to 968 where theinterrupts are disabled. The hangup box will then be checked todetermine if it is off hook as indicated at 972. If the result of thetest at 972 is negative, program flow will proceed directly to 976 andif the result is affirmative, the relays and call light will be clearedas indicated at 974. The program control will then be transferred to thePSK REC input of the START routine 976.

FIG. 20 shows a flow diagram of the TIMCHK routine of the mobile unitcomputer program and is entered as shown at 978. The program flowproceeds to block 980 where the interrupts are disabled and the programthen vectors program control to the proper routine as indicated byblocks 982, 984, 986, and 988. FIG. 21 shows the flow diagram of the EMRMON routine of the mobile unit computer program and, as indicated, thisroutine is entered at block 990. Program flow proceeds directly to block992 where the argument is checked to determine if it is equal to 0 andif the result is positive, program flow proceeds directly to block 994where the priority mode is stopped if it is on and then to block 996where program control is transferred to the PSK REC input of the STARTroutine. If the result of the test at 992 is negative, the priority modeis checked to determine if it is on as indicated at 998. If the prioritymode is not on, the PTT is disabled as indicated at 1202 and if it ison, the PTT is turned on as indicated at 1000. The program control thenadvances to block 1004 where the variable COUNT is set to equal theargument afterwhich the count is decremented at 1008. In addition, theroutine may be entered at this point at the entry point MONRPT indicatedat block 1006. Program flow will advance from block 1008 to block 1010where the count will be tested to determine if it is equal to 0. If notequal to 0, program flow will transfer directly to block 1014 and if itis equal to 0, then the program flow will continue to block 1012 wherethe PTT is turned off. The program control will then transfer to the PSKinput of the START routine as indicated at block 1014.

A flow diagram of the TONES routine of the mobile unit computer programis shown in FIG. 22. The routine is entered at block 1020 as indicatedand program flow proceeds directly to block 1022 where the tone count isdecremented. The COUNT is then checked to determine if it is equal to 0at 1024 and if the result is positive, the program control istransferred to the PSK input of the START routine as indicated at 1026.If the test at 1024 is negative, the program flow proceeds to block 1028where the time out timer is set up after which the alert tone isgenerated, as indicated at 1030. Program flow then continues to block1032 where the transmission switch is checked to determine if it is on,and if it is, the program flow jumps back to block 1030 where a tone isgenerated. If the trans switch is not on, program flow proceeds to block1034 where a 300 millisecond wait occurs before returning to the STARTroutine at either the PSK or the PSK REC input.

In summary, an improved selective calling, priority, transmitter controlsystem, data signalling system particularly well adapted for use inmultiple unit radio communications systems, capable of both voice anddata communications, has been described.

While a preferred embodiment of the invention has been described indetail, it should be apparent, that many modifications and variationsthereto are possible, all of which fall within the true spirit and scopeof the invention.

                  APPENDIX I                                                      ______________________________________                                        The following is a memory dump of the computer                                program for the base unit MC6803 microcomputer according                      to the invention.                                                             ______________________________________                                        :1080000028432920434F5059524947485420313979                                   :1080100038322C204D4F544F524F4C4120494E4343                                   :108020002E54494D204255524B4500010102010298                                   :10803000028301020283028383840102028302839A                                   :108040008384028383848384848501020203020380                                   :10805000038402030384038484850203038403846A                                   :108060008485038484858485858601020203020356                                   :10807000038402030384038484850203038403844A                                   :108080008485038484858485858602030304030430                                   :10809000048503040485048585860304048504851A                                   :1080A000858604858586858686870B0906030008F4                                   :1080B00005020A0704014F970897B686089700CE75                                   :1080C0000190B64817462505BD85F42003BD85F00F                                   :1080D000F668009602BD8F7E16C10C240FCE80AAD2                                   :1080E0003AE600D7A096A2850427043BD7C03B8E72                                   :1080F00000FFC10B2623D6A42B12853A261196A386                                   :108100008548260BC50B2607BD8D6C3F7E945ABD56                                   :10811000863FBD8D7DBD8D963F96A32BEE850826AF                                   :10812000EA96A4858126E496A285202713C10A2613                                   :10813000DAB64816850827D37300BF26CE7E862A76                                   :10814000851026C785082717C10A26BF96A4850271                                   :108150002607854026067E86807E86637E944A8535                                   :10816000022720DEC496A4850827026E00CE4800B0                                   :108170003AE600863FC1FF275ED7A1CE81E33AEE03                                   :10818000006E00C10A260F860297A297B57F00CE27                                   :10819000C630BD8C033F96B527064F5F97B5DDB35C                                   :1081A000DCB3BD8F79DAA08D21BD8D8DBD8D963F5D                                   :1081B000F6480BC4F0D79DF6480DC4F0D19D2609B2                                   :1081C000F6481158585858D19D39D7B48DE2260435                                   :1081D000840F9A9D97B3398E00FFBD860DCE93AB69                                   :1081E0007E939E821382B882FF832E8336833E83E2                                   :1081F0009A83B383BB83C383CB83D383DB83E38340                                   :10820000EB83F384058405849C83609352853B85CE                                   :10821000A193D7CE8252DFC6C610BD8C0386F097DD                                   :10822000A1CE8230DFC4CC0200DDA2860897A43F35                                   :1082300096A0810A26037E846FD6B527055FD7B541                                   :10824000D7A1D6A1BD8F79DAA0BD851EDDCABD8DAF                                   :108250001D3FBD82EF97BAD6B1C1EF271DD7B9CC6C                                   :10826000507DDDD1D6BABD851EDDCFCC0040DDA26C                                   :108270005FD7CEBD81CABD8D093FCE82A9DFC6CCF6                                   :108280000040DDCACC3871DDCCBD8D1DCE8297DFBC                                   :10829000C486EF97A1208FD6A0C10A26037E846FE3                                   :1082A000CAE0BD851E97CA20A596A181EF26058646                                   :1082B000667E81D797B920A786FF97BA96B181EFDE                                   :1082C000271C8AE097B9BD81B02717840F16BD859A                      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             :1098300081E0272096908D0FBD81B0260486209769                                   :1098400090BD9A837E97879791D793BD8F7E97908F                                   :10985000D7922032D79EBD8F7ED7928D29CC475295                                   :10986000DD9020DDCC2041DD90CC4C4CDD9220D130                                   :10987000BD81B027EFCE464CDF90C654D792840FFF                                   :109880008A30979320BBCE0090A600840F8A30A721                                   :1098900000088C009D26F239D6A186033D04CE9A9D                                   :1098A000CB3A8603BD97107E9787D689B648172ABC                                   :1098B0002AD78ECE0090CC20305C08A70076008E90                                   :1098C0002402E700C13826F1B64814851026048624                                   :1098D000209798CE009186087E9710D796BD8F7EF0                                   :1098E000D7958DA2DC95813A25028B07C13A2502D6                                   :1098F000CB07DD95CC5354DD91CC5320DD93D79726                                   :10990000D79820CFBD9A2FB648152B0CD68AC1E028                                   :109910002406BD91D12401399688F64815812A265E                                   :1099200007C52027F27E99B281442605C502263557                                   :10993000394D2607C50427DF7E99C78101274EC50B                                   :109940000827D4810E260EBD99D9BD99E4D689BDCC                                   :1099500098547E97E98105270E8103262BF648143B                                   :10996000C520261B398D0A8D708D79BD98AA7E97EA                                   :10997000E9B6481D85402706BD9265240138398D1A                                   :10998000588D61BD989820CA810427DB398DE2FC8F                                   :109990004814C50127E84D2ACE96892A0E8D3ACE65                                   :1099A0009B31BD98A2BD98AA7E97E98D2CCE9B34A1                                   :1099B00020F08D259689270ACE9ACBBD98A2DC8A05                                   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             :109A90000E034F5249472020204445535420202094                                   :109AA000202054494D4520202020202020204441C2                                   :109AB000544520202020202046434E2020202053A3                                   :109AC0005441545553204641494C2053435353432A                                   :109AD00045524F53524153534347434347445443E2                                   :109AE000455443444D43454D4353504150414750E5                                   :109AF000414743414C43414C554453504F535041CF                                   :109B0000535341535243484D4F4E5343485052498B                                   :109B10005458204E5354414C54435354434752419C                                   :109B2000434B2020202020204C4F47204F4E4143C4                                   :109B30004B5458535458454A414E4645424D415264                                   :109B40004150524D41594A554E4A554C4155475343                                   :109B500045504F43544E4F5644454353544152543D                                   :109B60008E00FF7F40004F5FDDCADDCC97CEBD8DFC                                   :109B700022C64CBD8C038614BD861AC614D703CEEC                                   :109B80008869DF81CC080C9708D700CC019AD309EB                                   :109B9000DD0B0E8655979DBD885A20F7B64818856F                                   :109BA00004260E866DBD860DB65800492BFA7E89B7                                   :109BB0003D7F0008B740018605BD861AC650BD8CA2                                   :109BC00003BD8D8DCC04FF97A2D7A00EB6580049D7                                   :109BD0002B037E893DD6A0C1FF27F10FC10B27DCE7                                   :109BE00096A42704DEC46E0096A32712C1012603A3                                   :109BF0007E9C9CC10326037E9D49863F200EC10AA0                                   :109C000026C27300A3C654BD8C0320B88E00FFBDCE                                   :109C1000860DBD9C6F20A5CE008E5F8640B750009C                                   :109C2000F7600086034A26FDB6580043A700BD9F93                                   :109C30003686394A26FD08CB108C009E26DDCE00E4                                   :109C40008ED693E8002B0A088C009E26F4867C2092                                   :109C5000BBCE008E5F96932A02C630D784A60084BE                                   :109C60003098842606088C009E26F239BD8C03CEDF                                   :109C700017707E85F4DC88B3480D2508FC480B93EB                                   :109C800088250139865B2084968A270AB1481025E9                                   :109C900006B1480F220139864F7E9C0C861597032A                                   :109CA000BD9C17261186119703BD9C172608C65820                                   :109CB000BD8C037E9C12CE009DC602A6004848487B                                   :109CC00079008B79008A7900897900885A26F00911                                   :109CD0008C008D26E44F7900924979008F49978C4A                                   :109CE000C65C8D888D8FDC888D95438D82C660BD36                                   :109CF0009C6C8D94D68A8D42BD81B02610968B8443                                   :109D00000F8AE0B14811271486077E9C0CC664BDFB                                   :109D10009C6CD68BC40FC10A24EE8D1E968BBD8F12                                   :109D20007EB84819840F2705867F7E9C0CC670BDBF                                   :109D30009C6CD68C5C8D037E9BBCBD851EDDCA4FA2                                   :109D40005FDDCCBD8D1D7E9C6FC65CBD9C6C4F5F86                                   :109D5000DDA6BD9543CE9D61DFC486FF97A47E9BA3                                   :109D6000C4C10A2705BD950520F4DCA6DD88BD9C8D                                   :109D700075C610BD8C03CE9D7E7F00A120DAC10A7E                                   :109D80002711D6A1BD8F79DAA0BD851EDDCABD8D94                                   :109D90001D20CB96A1978ABD9C88BD81B02611F667                                   :109DA0004811C40FD78BC674BD8C03CE9DE520C966                                   :109DB000C664BD8C03860F97A1F64811C40FBD85FC                                   :109DC0001E97CAC640D7CBCC3871DDCCBD8D1DCE19                                   :109DD0009DD57E9D58C10A27035F20ABD6A1C11037                                   :109DE00025C07E9D08C10A27035F209BD6A12704BA                                   :109DF000C1052505866D7E9COC5AD78CF64819BD89                                   :109E00008F79DA8BD78BC678BD8C03CE9E117E9D61                                   :109E100058C10A27037E9BC4C668BD9C6C861597F3                                   :109E2000038D26861197038D20860297DFC615962F                                   :109E3000932A02C614D703378D2633C4FBD7038D6C                                   :109E40001F7A00DF26E77E9C9CBD9C17260D96920C                                   :109E500098932B07968F98932B0139867C7E9C0CC8                                   :109E60007F0084CE008B86049786E6005686108D90                                   :109E70002A5686208D2596844C81102614D68C86F1                                   :109E80000197845686308D13860497845686302039                                   :109E90000A97847A008626D40920CB373C9783869C                                   :109EA00003978596932B3224298D7786489A83B71A                                   :109EB0005000C6115A26FD8648B750008D72CE005C                                   :109EC000E80926FD8D78270E7A008526DC866F7ED0                                   :109ED0009C0C8D6A27F738333925418D458649B763                                   :109EE00050003D86499A83B75000C60A5A26FD8421                                   :109EF000F7B75000C6615A26FD8A08B75000C6065B                                   :109F00005A26FD8649B750003D8D25CE03590926B6                                   :109F1000FD8D2B26C17A008526C120B18D2026AD6E                                   :109F200020B48648B75000D684BD8F79F7600039D9                                   :109F30008608B750003D4FB75000B76000398640E3                                   :109F40008DE2C6035A26FDF658008DEA96838130CD                                   :089F50002703D58339C58039D0                                                   :109FF000893D893D0080893D80B689FF9B60893D10                                   :0000000000                                                                   ______________________________________                                    

                                      APPENDIX II                                 __________________________________________________________________________    The following is a memory dump the computer program                           for the mobile unit MC3870 according to the invention.                        __________________________________________________________________________    S 1 1 B 0 0 0 0 1 A 2 8 0 5 D 6 B 0 B 1 B 6 5 1 2 8 0 0 8 A 2 8 0 6 A 3 6     A 7 1 5 C 6 F 7 3 5 D 6 7 F 7 5 D 7 2 3 9                                     S 1 1 B 0 0 1 8 5 D 4 4 5 C 2 9 0 1 2 0 5 3 4 E 1 E 0 5 A 0 5 2 3 4 8 1 1     7 E 3 9 1 0 5 2 0 6 9 9 0 0 5 4 2 5 3 D 7                                     S 1 1 B 0 0 3 0 2 0 6 4 B 7 4 1 1 8 5 1 7 1 5 4 3 8 0 1 1 D 1 B 1 C E 3 8     1 0 7 4 2 5 3 2 0 6 D 9 0 0 3 2 0 6 F C E                                     S 1 1 B 0 0 4 8 B 7 4 2 E 1 5 2 C 2 4 5 1 9 C 5 5 5 3 8 0 1 1 D 1 B 1 C 4     2 1 3 C 0 5 2 2 1 6 5 5 B 1 0 7 1 8 A 5 6                                     S 1 1 B 0 0 6 0 5 0 4 5 1 F 2 5 2 6 9 4 0 3 2 0 1 8 5 5 0 B 7 1 F 0 C C C     C 5 C 7 0 1 9 1 C 7 0 5 2 5 4 7 7 5 A 7 6                                     S 1 1 B 0 0 7 8 2 0 1 7 5 5 2 0 3 8 5 4 1 C A 5 1 4 5 0 A 4 1 2 2 1 7 0 E     0 0 5 7 0 1 C 5 4 5 A 4 1 2 1 7 0 1 3 A 3                                     S 1 1 2 0 0 9 0 E E B 4 7 8 5 0 4 1 1 5 1 F B 5 E 0 B 5 E 0 B 5 7 0 B 5 1     C 5 E                                                                         S 1 1 B 0 0 A 0 1 A 2 8 0 6 A 3 C 7 7 4 8 1 0 2 B 5 5 8 7 3 5 1 2 8 0 5 7     5 2 8 0 5 6 D 8 4 6 3 A 6 8 4 6 0 2 8 F S                                     S 1 1 B 0 0 B 8 0 5 D A 4 6 1 2 1 5 8 1 3 1 A 1 9 1 0 A 1 3 1 3 8 1 0 E 6     7 6 A 4 C 9 0 0 3 2 0 F F 0 7 7 F F 5 F 2                                     S 1 1 B 0 0 D 0 2 2 E 0 0 6 2 0 2 A 0 4 2 0 1 0 0 5 2 8 0 6 0 C 2 0 2 A 0     4 7 0 0 5 2 8 0 5 7 1 2 8 0 6 0 C 0 2 B 2                                     S 1 1 B 0 0 E 8 1 4 2 3 0 E 9 4 2 A 2 8 0 6 D F 6 B 6 7 7 4 F 6 F C 9 4 2     0 7 4 5 C 7 1 F 6 8 4 0 B 0 4 2 0 8 0 9 6                                     S 1 1 B 0 1 0 0 5 1 2 8 0 5 E A 2 8 0 6 0 C 7 2 F 6 8 4 0 C 2 8 0 5 7 1 7     1 0 4 2 8 0 5 E 8 2 8 0 6 0 C 2 8 0 5 B A                                     S 1 1 B 0 1 1 8 7 1 B 5 B 6 7 F 5 1 2 8 0 5 6 3 6 5 6 8 A 0 5 C 7 8 E C 2     1 0 8 1 2 1 2 F 7 5 0 6 A 7 C F C C 0 2 C                                     S 1 1 B 0 1 3 0 5 E A 1 5 C 4 6 1 3 9 1 0 5 4 C 1 2 1 3 5 C 6 7 6 8 4 D 5     0 4 C 5 1 2 8 0 - D F 4 E C C 7 0 9 4 6 8                                     S 1 1 B 0 1 4 8 0 6 C 7 7 1 8 1 0 2 4 0 2 2 2 E B 6 6 8 5 C B 6 7 2 F C 6     5 6 A 9 4 0 8 C 1 8 4 0 5 7 8 F 6 9 4 0 6                                     S 1 1 B 0 1 6 0 0 6 5 1 7 D F C C 1 5 C 4 C B 4 7 0 6 F 6 0 5 C 6 3 5 C 6     2 5 D 8 F F 9 0 7 6 B 2 0 1 7 5 D 7 1 7 E                                     S 1 1 B 0 1 7 8 5 C 7 4 5 8 7 7 5 A B 7 1 B 9 0 3 2 6 3 C 0 4 C 1 9 8 2 0     3 C C 5 C 4 E 8 F F 8 6 2 6 9 4 B 1 2 A C                                     S 1 1 B 0 1 9 0 E B 1 4 2 1 0 1 5 0 7 E F B 8 4 0 7 2 3 0 E 8 4 0 3 3 0 3     0 4 C C 0 9 1 0 8 2 5 1 4 8 1 0 3 2 0 4 4                                     S 1 1 B 0 1 A 8 1 4 5 C 4 D C C 2 0 F 6 8 2 0 2 1 3 5 C 7 0 C 8 8 1 F D 7     4 5 8 0 2 E 5 5 0 4 5 0 6 7 1 3 6 8 1 7 D                                     S 1 1 B 0 1 C 0 3 A E 4 0 2 8 4 0 2 1 2 5 B 7 1 5 6 F 0 8 4 0 8 3 7 1 8 E     7 9 4 0 3 5 7 3 8 1 0 0 3 1 3 1 6 5 0 E 5                                     S 1 1 B 0 1 D 8 6 C 8 4 A 7 6 2 3 C 7 7 F E 4 C 9 4 0 9 1 F 2 5 2 6 9 4 0     4 2 9 0 2 E 3 5 C 0 B 0 0 E 0 5 0 C 0 1 1                                     S 1 1 B 0 1 F 0 4 C 1 9 C C 5 C 6 2 6 9 9 0 B 0 9 0 B 9 F 0 8 4 0 A C 7 5     7 7 2 E 7 9 4 0 4 5 7 7 5 5 8 6 3 6 8 9 6                                     S 1 1 B 0 2 0 8 2 0 0 7 E D 5 B 1 0 1 6 5 0 4 D 2 3 0 9 5 B 1 0 1 6 C 0 5     0 4 D 2 3 2 A 5 B 1 0 1 6 C 0 5 0 4 D 7 3                                     S 1 1 B 0 2 2 0 2 3 4 4 5 B 1 0 1 6 C 0 5 0 4 C 2 3 6 F 5 B 1 0 1 6 C 0 1     3 2 5 0 A 8 2 0 6 2 5 4 4 8 2 0 5 1 8 D 9                                     S 1 1 B 0 2 3 8 0 4 7 7 0 7 6 2 6 F 3 C 4 C 6 6 8 4 3 1 2 1 1 F 9 4 4 4 0     3 1 3 9 4 1 C C C 8 4 0 B 3 E 9 4 0 4 A 5                                     S 1 1 B 0 2 5 0 2 9 0 4 D 9 4 E C E 9 4 0 F 6 5 6 8 A 0 5 0 4 D E 0 1 5 9     1 4 5 A 1 5 B E C 9 4 5 1 6 2 6 A 7 F E 0                                     S 1 1 B 0 2 6 8 C C 6 5 4 C 9 1 0 3 2 2 0 2 B 4 9 0 8 7 6 5 4 E E C 5 E B     0 7 0 3 E 9 4 0 2 7 4 3 E 9 4 0 5 3 E 0 0                                     S 1 1 B 0 2 8 0 9 4 0 2 7 8 6 A 1 8 F C 5 C 9 0 D D 6 8 7 4 F C 6 E C E 9     4 D 6 A 0 1 3 8 1 0 4 2 9 0 4 A 9 7 0 1 1                                     S 1 1 B 0 2 9 8 C E C C 9 4 C A A 0 1 3 1 3 8 1 C 5 2 9 0 4 E D 1 A 4 0 1     5 8 1 0 7 2 8 0 5 D 6 B 0 B 1 B 6 2 8 F 3                                     S 1 1 B 0 2 B 0 0 6 A 3 2 9 0 1 2 0 5 0 4 B 5 C F 0 8 4 A B 1 A 2 8 0 6 D     F 4 6 1 3 9 1 1 1 7 1 F B 9 4 E 3 C 6 5 E                                     S 1 1 B 0 2 C 8 8 1 1 7 1 3 1 3 9 1 0 6 4 0 2 1 F 8 8 4 0 E 4 7 1 3 8 1 0     4 2 9 0 4 E D 6 5 6 A 7 C F C 1 F 5 C 1 F                                     S 1 1 B 0 2 E 0 2 9 0 1 3 B 1 A 2 8 0 0 7 3 3 4 3 4 2 8 0 0 6 1 5 0 2 8 0     0 5 6 E 0 C 3 C 3 5 3 2 1 5 3 5 B 1 0 9 1                                     S 1 1 B 0 2 F 8 7 7 8 A 2 5 0 2 8 2 0 9 4 3 2 3 1 3 5 3 4 2 2 3 4 0 5 2 4     2 1 3 5 B C B 6 2 6 D 4 C 1 9 8 2 0 3 4 0                                     S 1 1 B 0 3 1 0 C C 5 C 4 E 8 F F 8 3 4 9 4 D 2 2 8 0 5 9 C 4 4 E D 9 4 C     2 4 5 E C 9 4 B E 2 8 0 6 A 3 4 C 5 8 F 2                                     S 1 1 B 0 3 2 8 6 2 6 8 2 0 2 0 E D 5 B 2 1 B F 5 0 4 D 5 1 0 4 4 D 0 6 4     E 0 7 7 0 5 4 C 8 9 4 0 4 C 0 8 4 2 6 5 F                                     S 1 1 B 0 3 4 0 7 F F 5 2 2 E 0 E C 9 4 0 7 3 4 6 7 4 C 6 2 9 0 0 7 4 2 5     A 2 8 0 5 4 C 4 3 6 B 5 A 2 8 0 5 4 C 2 E                                     S 1 1 B 0 3 5 8 5 9 C 8 8 4 0 D 7 0 C 4 9 4 8 1 C 0 9 4 F C 7 6 5 0 2 9 0     5 1 C 6 5 6 A 4 6 1 5 8 1 5 F 7 A E 0 C A                                     S 1 1 B 0 3 7 0 9 4 5 6 C 1 8 4 7 E 2 1 1 0 8 4 0 A F 7 4 C 8 4 0 3 2 2 0     1 2 1 0 D 5 C 7 F F 1 8 4 4 D 1 5 8 1 B 7                                     S 1 1 B 0 3 8 8 0 B 4 C 2 2 0 C 5 D 2 0 2 3 5 D 5 D 7 F 5 C 6 F 7 4 F 1 8     4 0 D 7 0 C 4 4 C 9 4 0 3 2 2 0 1 5 E A 2                                     S 1 1 B 0 3 A 0 4 C 2 2 0 1 5 D 4 1 1 F 2 1 0 2 8 4 6 8 F 1 1 2 1 5 1 F 6     6 5 C 6 A 5 D 6 C 4 C 5 2 7 0 5 D 5 D 1 2                                     S 1 1 B 0 3 B 8 6 8 5 E C 2 8 4 5 5 6 5 4 C 2 2 0 4 5 C 6 A 7 D F C 9 0 4     A 7 E E 0 4 1 8 4 4 4 7 5 E 0 9 4 0 A 7 E                                     S 1 1 B 0 3 D 0 7 8 F 7 8 4 4 1 2 8 0 0 8 A 9 0 3 9 7 2 E 0 9 4 4 0 7 4 E     1 8 4 1 7 7 5 E 1 8 4 6 C 7 E E 1 9 4 1 3                                     S 1 1 B 0 3 E 8 3 6 4 6 1 5 8 1 1 4 6 7 4 C 0 5 9 0 6 6 7 C F C 5 C 9 0 7     0 C 6 8 1 7 0 2 8 0 5 E 8 9 0 5 9 C 6 D 6                                     S 1 1 B 0 4 0 0 8 1 6 8 6 E 4 C 2 2 0 4 5 D B 0 7 1 F C 5 C 9 0 6 7 7 1 6     8 6 7 5 C 2 0 4 0 F B 8 4 5 4 7 3 0 4 0 4                                     S 1 1 B 0 4 1 8 7 9 9 5 9 0 3 C 7 3 E 0 9 4 4 A c 1 9 1 0 D 6 6 6 C 7 0 C     C 8 4 4 1 2 8 0 5 E 1 3 9 9 0 4 5 2 4 E 4                                     S 1 1 B 0 4 3 0 7 A 8 4 7 7 1 F 8 4 E 1 1 F 8 4 C 7 1 F 8 4 D 3 1 F 8 4 C     F 7 8 F 6 8 4 2 7 4 1 2 4 7 F 8 4 0 5 D F                                     S 1 1 B 0 4 4 8 1 F 9 4 1 F 7 2 6 9 3 9 9 0 C 0 4 7 1 5 8 1 1 6 2 8 0 0 7     F 7 F 5 1 2 8 0 5 7 5 2 8 0 6 0 C 4 C D 0                                     S 1 1 B 0 4 6 0 B 5 7 0 B 6 C 9 8 4 0 4 2 9 0 1 2 0 2 9 0 1 3 B 6 A 3 C 9     1 F A 6 F 7 F 5 C 7 6 5 1 2 8 0 5 6 6 D 0                                     S 1 1 B 0 4 7 8 5 2 5 0 7 1 5 3 2 0 1 4 5 1 5 1 2 0 C 0 1 F 9 4 F 3 7 C F     C 2 2 1 1 B 4 7 8 E 0 5 0 B 5 4 6 1 3 8 6                                     S 1 1 B 0 4 9 0 9 1 0 6 A 1 2 1 0 1 9 4 5 4 A 0 1 3 9 1 0 F 1 3 9 1 D F 3     2 9 4 E 0 3 3 8 1 D D 2 8 0 5 6 3 9 0 E 1                                     S 1 1 B 0 4 A 8 B 9 1 A 6 5 6 E 4 C 2 2 4 0 5 C B 0 2 8 0 6 A 3 5 8 2 0 1     5 5 C 6 8 7 2 5 C B 5 5 1 2 8 0 5 7 5 4 0                                     S 1 1 B 0 4 C 0 6 6 6 E 3 C 8 4 5 8 2 8 0 5 C 4 2 8 0 5 E 8 7 8 F 7 8 4 0     4 2 8 0 0 7 F 0 4 1 4 5 8 7 1 5 9 9 0 C 6                                     S 1 1 B 0 4 D 8 8 4 1 A 2 8 0 6 A 3 5 1 5 9 C E 9 4 E 0 C E 9 4 4 4 C C 9     4 2 1 9 0 8 3 2 9 0 2 A 9 1 A 2 8 0 6 5 7                                     S 1 1 B 0 4 F 0 A 3 C 6 8 1 3 E 2 8 0 5 D 6 6 8 7 2 B 5 5 C 2 8 0 5 E 8 7     4 F 7 2 4 0 2 5 C 7 F 5 1 2 8 0 5 6 3 7 8                                     S 1 1 B 0 5 0 8 2 3 0 1 8 4 3 2 2 8 0 5 C 4 A 0 1 2 1 5 8 1 1 E 6 C 3 E 4     C 0 5 2 0 4 4 9 0 B 7 2 8 0 5 E 1 C 1 3 1                                     S 1 1 B 0 5 2 0 8 4 1 3 6 D 5 C 6 8 4 0 5 C B 5 6 D 3 C 6 F 7 F 9 4 0 3 7     0 5 D 5 C 2 9 0 1 3 B 6 5 6 E 7 5 F C A 6                                     S 1 1 B 0 5 3 8 5 C B 0 2 9 0 1 2 0 2 8 0 5 E 1 6 5 4 C 2 2 0 4 5 C 4 7 1     3 9 1 F 2 2 9 0 2 D A 4 A E C 8 4 1 3 6 1                                     S 1 1 B 0 5 5 0 3 4 4 A 2 2 0 F E C 8 4 0 C 4 A 2 2 F 0 E C 8 4 0 6 2 0 F     F E C 9 4 D 0 1 C 7 2 9 0 0 3 2 0 1 0 D 2                                     S 1 1 B 0 5 6 8 5 2 7 4 5 8 9 0 0 C 2 0 1 0 9 0 0 2 7 0 5 B 7 0 5 1 2 0 1     2 5 2 7 0 6 0 6 5 6 A 7 C F C C 2 B 4 6 E                                     S 1 1 B 0 5 8 0 A 0 1 4 F 8 8 4 0 4 2 9 0 4 A 9 C 1 9 4 0 A A 0 F B 9 4 0     5 A 6 9 1 E 7 5 5 1 C 3 0 9 4 E 4 3 1 5 A                                     S 1 1 B 0 5 9 8 9 4 E 1 7 0 1 C 6 2 6 8 7 0 5 4 5 5 4 D E 4 5 3 1 2 1 2 1     2 5 1 E 5 5 4 4 3 1 4 E 3 5 5 1 5 5 2 2 9                                     S 1 1 B 0 5 B 0 1 3 E 5 5 5 4 1 1 4 E 2 E 4 5 4 0 A 2 5 1 4 9 4 E 5 4 4 1     8 5 4 4 5 1 8 5 5 1 C A 7 2 1 0 3 5 0 1 E                                     S 1 1 B 0 5 C 8 4 5 1 4 1 3 2 4 0 6 5 1 C 1 3 0 8 1 F D 6 6 6 F 5 C 1 C 6     7 6 8 7 0 5 C 6 5 6 A 7 0 5 C 6 E 5 D 7 0                                     S 1 1 B 0 5 E 0 5 C 6 6 6 F 7 0 5 D 8 F F E 1 C 7 0 5 1 6 5 6 E 4 C 2 2 2     0 B 0 A 1 5 0 4 E B 0 4 6 C 6 7 0 9 2 8 9                                     S 1 1 B 0 5 F 8 0 E 4 0 9 1 0 C 1 2 5 0 2 0 2 0 F 6 4 0 9 4 0 3 1 2 1 2 C     1 6 6 6 B 5 D 0 5 1 C 1 A 7 6 B 5 6 2 B 2                                     S 1 1 B 0 6 1 0 6 8 0 0 5 D 0 1 5 D 0 2 5 D 0 3 5 C 0 8 4 5 1 2 2 1 7 8 1     F 5 1 2 8 0 5 7 5 2 8 0 5 9 C 4 4 5 D 7 9                                     S 1 1 B 0 6 2 8 4 5 5 C 2 8 0 0 7 3 6 2 6 D 1 3 4 C 1 9 8 2 0 3 C C 5 C 4     E 8 F F 8 7 0 1 9 5 0 2 8 0 0 6 1 2 8 1 7                                     S 1 1 B 0 6 4 0 0 0 5 6 3 4 9 4 E 9 6 2 6 8 2 A 0 2 0 2 2 0 5 5 5 D 5 D 5     D 7 7 8 E 1 6 8 F F 5 5 E 6 5 4 C 5 0 0 F                                     S 1 1 B 0 6 5 8 6 A 4 C 2 2 1 2 5 1 6 2 6 8 7 5 5 2 7 8 5 3 5 4 3 4 9 4 F     E 4 1 1 8 5 1 E C 1 4 1 3 1 4 1 3 E 0 1 1                                     S 1 1 B 0 6 7 0 B 0 A 0 1 4 F 8 8 4 0 4 2 9 0 4 A 9 2 0 1 C 3 2 9 4 E 6 7     5 5 2 4 C C C 1 9 5 C D B 2 0 1 9 3 3 3 1                                     S 1 1 B 0 6 8 8 9 4 D A 7 8 5 3 4 1 B 4 D B 0 A 1 F 0 B 2 5 2 6 2 0 1 5 9     4 C C 6 6 6 8 7 0 C 7 4 C 8 1 0 3 2 2 4 2                                     S 1 1 B 0 6 A 0 0 4 B 5 0 C 6 6 6 8 4 E 5 9 6 0 7 0 5 D 8 F F E 6 9 1 F C     9 B 5 7 3 F 0 8 4 0 5 4 C 1 3 1 3 5 E 8 8                                     S 1 1 B 0 6 B 8 4 D A 4 1 4 1 2 5 1 7 1 F 1 C 7 8 2 0 3 C 7 5 7 4 6 1 9 C     6 5 6 7 6 F 1 1 2 E C 5 C 4 0 1 F 5 0 0 7                                     S 1 1 B 0 6 D 0 1 5 9 4 D B 4 9 B 5 6 7 6 C 4 2 5 D 4 3 5 D 4 6 5 D 4 7 5     C 6 7 6 C 4 D 0 6 4 D 0 7 4 D 5 6 4 E C 9                                     S 1 1 B 0 6 E 8 5 7 6 6 7 0 1 C 2 8 4 3 2 9 2 0 4 2 5 9 2 0 4 D 4 F 5 4 4     F 5 2 4 F 4 C 4 1 2 0 3 1 3 9 3 8 3 1 D E                                     S 1 1 B 0 7 0 0 0 0 0 1 0 1 0 2 0 1 0 2 0 2 8 3 0 1 0 2 0 2 8 3 0 2 8 3 8     3 8 4 0 1 0 2 0 2 8 3 0 2 8 3 8 3 8 4 2 9                                     S 1 1 B 0 7 1 8 0 2 8 3 8 3 8 4 8 3 8 4 8 4 8 5 0 1 0 2 0 2 0 3 0 2 0 3 0     3 B 4 0 2 0 3 0 3 8 4 0 3 8 4 8 4 8 5 7 9                                     S 1 1 B 0 7 3 0 0 2 0 3 0 3 8 4 0 3 8 4 8 4 8 5 0 3 8 4 8 4 8 5 8 4 8 5 8     5 8 6 0 1 0 2 0 2 0 3 0 2 0 3 0 3 8 4 5 9                                     S 1 1 B 0 7 4 8 0 2 0 3 0 3 8 4 0 3 8 4 8 4 8 5 0 2 0 3 0 3 8 4 0 3 8 4 8     4 8 5 0 3 8 4 8 4 8 5 8 4 8 5 8 5 8 6 B 9                                     S 1 1 B 0 7 6 0 0 2 0 3 0 3 0 4 0 3 0 4 0 4 8 5 0 3 0 4 0 4 8 5 0 4 8 5 8     5 8 6 0 3 0 4 0 4 8 5 0 4 8 5 8 5 8 6 9 9                                     S 1 1 B 0 7 7 8 0 4 8 5 8 5 8 6 8 5 8 6 8 6 8 7 0 1 0 2 0 2 0 3 0 2 0 3 0     3 8 4 0 2 0 3 0 3 8 4 0 3 8 4 8 4 8 5 0 9                                     S 1 1 B 0 7 9 0 0 2 0 3 0 3 8 4 0 3 8 4 8 4 8 5 0 3 8 4 8 4 8 5 8 4 8 5 8     5 8 6 0 2 0 3 0 3 0 4 0 3 0 4 0 4 8 5 F 1                                     S 1 1 B 0 7 A 8 0 3 0 4 0 4 8 5 0 4 8 5 8 5 8 6 0 3 0 4 0 4 8 5 0 4 8 5 8     5 8 6 0 4 8 5 8 5 8 6 8 5 8 6 8 6 8 7 4 1                                     S 1 1 B 0 7 C 0 0 2 0 3 0 3 0 4 0 3 0 4 0 4 8 5 0 3 0 4 0 4 8 5 0 4 8 5 8     5 8 6 0 3 0 4 0 4 8 5 0 4 8 5 8 5 8 6 3 9                                     S 1 1 B 0 7 D 8 0 4 8 5 8 5 8 6 8 5 8 6 8 6 8 7 0 3 0 4 0 4 0 5 0 4 0 5 0     5 8 6 0 4 0 5 0 5 8 6 0 5 8 6 8 6 8 7 8 9                                     S 1 1 3 0 7 F 0 0 4 0 5 0 5 8 6 0 5 8 6 8 6 8 7 0 5 8 6 8 6 8 7 8 6 8 7 8     7 8 8 1 5                                                                     S 9 0 3 0 0 0 0 F C                                                           __________________________________________________________________________

What is claimed is:
 1. In a communications system, for voicecommunications over a communications medium, having a primary stationincluding an address entry port, and a plurality of remote stations,each remote station having a predetermined station address stored in astation address register, a method of automatic selective calling,comprising the steps of:(a) at the primary station:(i) entering adesired station address into the address port; (ii) asynchronouslytransmitting, automatically, a preambled command signal containing apredetermined control code and the desired station address in responseto initiating a voice transmission; (iii) transmitting, automatically, apostambled command signal containing a second predetermined code, andthe desired station address in response to the conclusion of thevariable length voice transmission; (b) at each of said remotestations(i) receiving said transmitted first command signal; (ii)detecting when the desired station address contained in the receivedpreambled command signal is the same as the predetermined stationaddress stored in the station address register and unmuting the remotestation receiver in response thereto; (iii) receiving said transmittedsecond command signal; (iv) detecting when the desired station addresscontained in the received postambled command signal is the same as thepredetermined station address stored in the station register and mutingthe remote station receiver in response thereto.
 2. In a communicationssystem for voice communications over a communications medium, having aprimary station and a plurality of remote stations, each remote stationhaving a predetermined station address stored in a station addressregister, a method of priority calling comprising the steps of:(a) atthe remote station;(i) transmitting a command signal containing apredetermined control code, and the predetermined station address; (b)at the primary station;(i) receiving said transmitted command signal andtransmitting an acknowledge command packet, in response thereto, havinga preselected control code and the predetermined station address of thereceived command signal; (ii) activating an alarm at the primary stationin response to receiving the transmitted command signal.
 3. The methodof claim 2 further comprising the step, at the remote station, ofretransmitting the command packet a predetermined number of times untilthe acknowledge command packet is received.
 4. The method of claim 2further comprising the step, at the remote station, of activating thetransmitter of the remote station for a predetermined time period inresponse to receiving the acknowledge command packet from the primarystation,whereby voice conversations may be monitored as, for example,during an emergency.
 5. In a communications system for priority callingas claimed in claim 2 further comprising a method of transmitter controlcomprising the steps of:(a) at the primary station:(i) entering adesired station address to the address entry port; (ii) transmitting acommand signal containing a predetermined control code; (b) at otherremote stations;(i) receiving said transmitted command signal; (ii)detecting when the desired station address contained in the receivedcommand signal is the same as the predetermined station address storedin the station address register and disabling the remote station voicetransmission in response thereto,whereby other remote stations aredisabled from interfering with said monitored emergency.